PPC: Migrate from 'regset_from_core_section' to 'iterate_over_regset_sections'

PPC: Migrate from 'regset_from_core_section' to 'iterate_over_regset_sections'

For PPC targets, no longer define the gdbarch method
'regset_from_core_section', but the iterator method instead.

gdb/ChangeLog:

	* configure.tgt (gdb_target_obs): Add fbsd-tdep.o for PowerPC
	FreeBSD targets.
	* ppcfbsd-nat.c (_initialize_ppcfbsd_nat): Do not set target
	method 'make_corefile_notes'.
	* ppcfbsd-tdep.c (fbsd-tdep.h): Include.
	(ppcfbsd_regset_from_core_section): Remove.
	(ppcfbsd_iterate_over_regset_sections): New.
	(ppcfbsd_init_abi): Call fbsd_init_abi.  Adjust gdbarch
	initialization.
	* ppcnbsd-tdep.c (ppcnbsd_regset_from_core_section): Remove.
	(ppcnbsd_iterate_over_regset_sections): New.
	(ppcnbsd_init_abi): Adjust.
	* ppcobsd-tdep.c (ppcobsd_regset_from_core_section): Remove.
	(ppcobsd_iterate_over_regset_sections): New.
	(ppcobsd_init_abi): Adjust.
	* rs6000-aix-tdep.c (rs6000_aix_regset_from_core_section): Remove.
	(rs6000_aix_iterate_over_regset_sections): New.
	(rs6000_aix_init_osabi): Adjust.