Add 'regset' parameter to 'iterate_over_regset_sections_cb'

Add 'regset' parameter to 'iterate_over_regset_sections_cb'

This adds the 'regset' parameter to the iterator callback.
Consequently the 'regset_from_core_section' method is dropped for all
targets that provide the iterator method.

This change prepares for replacing regset_from_core_section
everywhere, thereby eliminating one gdbarch interface.  Since the
iterator is usually no more complex than regset_from_core_section
alone, targets that previously didn't define core_regset_sections will
then gain multi-arch capable core file generation support without
increased complexity.

gdb/ChangeLog:

	* gdbarch.sh (iterate_over_regset_sections_cb): Add regset
	parameter.
	* gdbarch.h: Regenerate.
	* corelow.c (sniff_core_bfd): Don't sniff if gdbarch has a regset
	iterator.
	(get_core_register_section): Add parameter 'regset' and use it, if
	set.  Add parameter 'min_size' and verify the bfd section size
	against it.
	(get_core_registers_cb): Add parameter 'regset' and pass it to
	get_core_register section.  For the "standard" register sections
	".reg" and ".reg2", set an appropriate default for human_name.
	(get_core_registers): Don't abort when the gdbarch has an iterator
	but no regset_from_core_section.  Add NULL/0 for parameters
	'regset'/'min_size' in calls to get_core_register_section.
	* linux-tdep.c (linux_collect_regset_section_cb): Add parameter
	'regset' and use it instead of calling the
	regset_from_core_section gdbarch method.
	* i386-tdep.h (struct gdbarch_tdep): Add field 'fpregset'.
	* i386-tdep.c (i386_supply_xstateregset)
	(i386_collect_xstateregset, i386_xstateregset): Moved to
	i386-linux-tdep.c.
	(i386_regset_from_core_section): Drop handling for .reg-xfp and
	.reg-xstate.
	(i386_gdbarch_init): Set tdep field 'fpregset'.  Enable generic
	core file support only if the regset iterator hasn't been set.
	* i386-linux-tdep.c (i386_linux_supply_xstateregset)
	(i386_linux_collect_xstateregset, i386_linux_xstateregset): New.
	Moved from i386-tdep.c and renamed to *_linux*.
	(i386_linux_iterate_over_regset_sections): Add regset parameter to
	each callback invocation.  Allow any .reg-xstate size when reading
	from a core file.
	* amd64-tdep.c (amd64_supply_xstateregset)
	(amd64_collect_xstateregset, amd64_xstateregset): Moved to
	amd64-linux-tdep.c.
	(amd64_regset_from_core_section): Remove.
	(amd64_init_abi): Set new tdep field 'fpregset'.  No longer
	install an amd64-specific regset_from_core_section gdbarch method.
	* amd64-linux-tdep.c (amd64_linux_supply_xstateregset)
	(amd64_linux_collect_xstateregset, amd64_linux_xstateregset): New.
	Moved from amd64-tdep.c and renamed to *_linux*.
	(amd64_linux_iterate_over_regset_sections): Add regset parameter
	to each callback invocation.  Allow any .reg-xstate size when
	reading from a core file.
	* arm-linux-tdep.c (arm_linux_regset_from_core_section): Remove.
	(arm_linux_iterate_over_regset_sections): Add regset parameter to
	each callback invocation.
	(arm_linux_init_abi): No longer set the regset_from_core_section
	gdbarch method.
	* ppc-linux-tdep.c (ppc_linux_regset_from_core_section): Remove.
	(ppc_linux_iterate_over_regset_sections): Add regset parameter to
	each callback invocation.
	(ppc_linux_init_abi): No longer set the regset_from_core_section
	gdbarch method.
	* s390-linux-tdep.c (struct gdbarch_tdep): Remove the fields
	gregset, sizeof_gregset, fpregset, and sizeof_fpregset.
	(s390_regset_from_core_section): Remove.
	(s390_iterate_over_regset_sections): Add regset parameter to each
	callback invocation.
	(s390_gdbarch_init): No longer set the regset_from_core_section
	gdbarch method.  Drop initialization of deleted tdep fields.