libmpeg2: Decode only Y on grayscale targets. The chroma skip code is probably less than optimal since it's basically the decoding code with minimum reading of the bitstream but it does the trick for now and gets some more FPS.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@16093 a1c6a512-1295-4272-9138-f99709370657

apps/plugins/mpegplayer/alloc.c

@@ -144,7 +144,7 @@ bool mpeg_alloc_init(unsigned char *buf, size_t mallocsize)
         return false;
     }
 
-    IF_COP(flush_icache());
+    IF_COP(invalidate_icache());
     return true;
 }