ppc: Various minor compile fixes

This fixes up a variety of minor problems in compiling with ARCH=ppc
arising from using the merged versions of various header files.
A lot of the changes are just adding #include <asm/machdep.h> to
files that use ppc_md or smp_ops_t.

This also arranges for us to use semaphore.c, vecemu.c, vector.S and
fpu.S from arch/powerpc/kernel when compiling with ARCH=ppc.

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