asm: Minor pixel_ssim_end4 improvements

Reduce the number of vector registers used from 7 to 5.
Eliminate some moves in the AVX implementation.
Avoid bypass delays for transitioning between int and
float domains.

Ported from Henrik Gramner's recent commit to x264
x86inc: Make INIT_CPUFLAGS support an arbitrary number of cpuflags

Ported from Henrik Gramner's recent commit to x264
framefilter: move SAO init logic into the frame filter
sao: don't pass member variables to functions

--HG--
extra : rebase_source : e1b8a13cfe4910f1235ead7952caa60942b0710c
pattern: use isLuma instead of restricted TextType range
types: remove generic TEXT_CHROMA enum, no longer used
common: rename QP range macros to be consistent with x264

I find QP_MAX_SPEC to be a lot more self-explanatory than MAX_QP
rc: rename m_bframes to m_leadingBframes

--HG--
branch : stable
rc: fix bitrate accuracy for vbv in fast presets.

--HG--
branch : stable
Merge with stable