PowerPC64 ELFv2 ABI: no function descriptors

PowerPC64 ELFv2 ABI: no function descriptors

This implements the most significant difference with the ELFv2 ABI:
we no longer use function descriptors.  The patch consists mostly
of switching off code to deal with descriptors :-)

In addition, when calling an inferior function, we no longer need
to provide its TOC in r2.  Instead, ELFv2 code expects to be called
with r12 pointing to the code address itself.

gdb/ChangeLog:

	* ppc-linux-tdep.c (ppc_linux_init_abi): Only call
	set_gdbarch_convert_from_func_ptr_addr and
	set_gdbarch_elf_make_msymbol_special for ELFv1.
	* ppc-sysv-tdep.c (ppc64_sysv_abi_push_param): Only handle
	function descriptors on ELFv1.
	(ppc64_sysv_abi_push_dummy_call): Likewise.  On ELFv2,
	set up r12 at function entry.