Giving consistent names to IDCT/IWHT functions.

The idea is to have the following names for each transform size:

vp9_idct4x4_add
  vp9_idct4x4_1_add
  vp9_idct4x4_10_add
  vp9_idct4x4_16_add

vp9_idct8x8_add
  vp9_idct8x8_1_add
  vp9_idct8x8_10_add
  vp9_idct8x8_64_add

etc for 16x16, 32x32

The actual list of renames in this patch:

vp9_idct_add_lossless     -> vp9_iwht4x4_add
vp9_short_iwalsh4x4_add   -> vp9_iwht4x4_16_add
vp9_short_iwalsh4x4_1_add -> vp9_iwht4x4_1_add

vp9_idct_add            -> vp9_idct4x4_add
vp9_short_idct4x4_add   -> vp9_idct4x4_16_add
vp9_short_idct4x4_1_add -> vp9_idct4x4_1_add

Change-Id: I6f43f7437c68dd30cdd05d72e213765578ed30b1