Refactor PVQ codes for intra4x4

In 4x4 intra search for RDO, AV1 codes has been changed to
call av1_xform_quant() while ago, while PVQ did not but call
txfm and pvq_encode_helper() instead, which caused duplicated codes
and thus worse maintenance and testing.

This refactor also has fixed the long-sitting bug,
which we couldn't find before refactoring.

PSNR    PSNR-HVS  SSIM  FAST-SSIM  CIEDE 2000 MS-SSIM
-2.77   -2.62     -2.90 -4.07       -2.94     -2.63

Change-Id: I6e526123a64af810897962d11d53028719e82e16
1 file changed