powerpc: Merge various powermac-related header files.

Except for smu.h, which moved from asm-ppc64 to asm-powerpc, all
of these moved from asm-ppc to asm-powerpc.  In each case the
asm-ppc64 version (if there was one) was just a single line
including the asm-ppc version.

Signed-off-by: Paul Mackerras <paulus@samba.org>