Make local functions in vp9_dct.c static

This commit limits the scope of 1-D DCT and ADST functions within
vp9_dct.c and makes them static. This largely clears out the cross
referencing issue between vp9_dct.c and the SIMD optimizations.

Change-Id: If7cac478b11bb32328ccf70a9f60b709dad43d7f
2 files changed