Consistent names for FDCT functions.

Renames:
  fdct4_1d   -> fdct4
  fadst4_1d  -> fadst4
  fdct8_1d   -> fdct8
  fadst8_1d  -> fadst8
  fdct16_1d  -> fdct16
  fadst16_1d -> fadst16

"_1d" suffix is redundant, so removing it. The same will happen with idct
in the next change sets.

Change-Id: Ibf421cd2f569146c6079269df7a31819c098265e