The target register of first word loaded must be marked early-clobber.

Originally committed as revision 19536 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 18606 to svn://svn.ffmpeg.org/ffmpeg/trunk

PPC is normally big endian but has special little endian load/store
instructions.  Using these avoids a separate byteswap.  This makes the
vorbis decoder about 5% faster.  Not much else uses little-endian
read/write extensively.

GCC generates horrible PPC code for the default AV_[RW]B64 (which uses
a packed struct), so we override it with a plain pointer cast.

Originally committed as revision 18602 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 18304 to svn://svn.ffmpeg.org/ffmpeg/trunk