Use core regset iterators on Sparc Solaris

Use core regset iterators on Sparc Solaris

Remove native-only core file handling on Sparc Solaris.  Instead,
enable the sparc target generic core regset logic on Solaris by
providing appropriate register offset maps.

Thanks to Joel Brobecker for testing!

gdb/
	* config/sparc/sol2.mh (NATDEPFILES): Remove core-regset.o.
	* sparc-sol2-tdep.c: Include "regset.h".
	(sparc32_sol2_supply_core_gregset): New function.
	(sparc32_sol2_collect_core_gregset): Likewise.
	(sparc32_sol2_supply_core_fpregset): Likewise.
	(sparc32_sol2_collect_core_fpregset): Likewise.
	(sparc32_sol2_gregset, sparc32_sol2_fpregset): New variables.
	(sparc32_sol2_init_abi): Set tdep->gregset/sizeof_gregset and
	tdep->fpregset/sizeof_fpregset.
	* sparc64-sol2-tdep.c: Include "regset.h".
	(sparc64_sol2_supply_core_gregset): New function.
	(sparc64_sol2_collect_core_gregset): Likewise.
	(sparc64_sol2_supply_core_fpregset): Likewise.
	(sparc64_sol2_collect_core_fpregset): Likewise.
	(sparc64_sol2_gregset, sparc64_sol2_fpregset): New variables.
	(sparc64_sol2_init_abi): Set tdep->gregset/sizeof_gregset and
	tdep->fpregset/sizeof_fpregset.