Standardize on _ASM_POWERPC_... prefix for all #include
exclusion symbols.  Fixup all the non-compilers.

Signed-off-by: Jon Loeliger <jdl@freescale.com>
Signed-off-by: Kumar Gala <kumar.gala@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>