M68K: Migrate from 'regset_from_core_section' to 'iterate_over_regset_sections'

M68K: Migrate from 'regset_from_core_section' to 'iterate_over_regset_sections'

For m68k BSD and GNU/Linux targets, no longer define the gdbarch
method 'regset_from_core_section', but the iterator method instead.

gdb/ChangeLog:

	* m68kbsd-tdep.c (m68kbsd_regset_from_core_section): Remove.
	(m68kbsd_iterate_over_regset_sections): New.
	(m68kbsd_init_abi): Adjust gdbarch initialization.
	* m68klinux-tdep.c (m68k_linux_regset_from_core_section): Remove.
	(m68k_linux_iterate_over_regset_sections): New.
	(m68k_linux_init_abi): Adjust gdbarch initialization.