[POWERPC] Switch to generic compat_binfmt_elf code

This switches the CONFIG_PPC64 support for 32-bit ELF to use the
generic fs/compat_binfmt_elf.c implementation instead of our own
binfmt_elf32.c.  Since so much is the same between 32/64, there is
only one macro we have to define to make the generic support work out
of the box.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>