mpegaudiosp: More consistent names for ppc/x86 optimization files
ppc: More consistent names for H.264 optimizations files
ppc: util_altivec: Surround AltiVec-related code by appropriate ifdefs

This prevents non-AltiVec-enabled compilers from choking.
ppc: Move AltiVec utility headers out of AltiVec ifdefs

Now that the headers themselves have ifdef protection this is no
longer necessary and more consistent with normal include handling.
fft: Remove pointless #ifdefs around function declarations
ppc: More consistent arch initialization