x86: detect Bobcat, improve Atom optimizations, reorganize flags

The Bobcat has a 64-bit SIMD unit reminiscent of the Athlon 64; detect this
and apply the appropriate flags.

It also has an extremely slow palignr instruction; create a flag for this to
avoid massive penalties on palignr-heavy functions.

Improve Atom function selection and document exactly what the SLOW_ATOM flag
covers.

Add Atom-optimized SATD/SA8D/hadamard_ac functions: simply combine the ssse3
optimizations with the sse2 algorithm to avoid pmaddubsw, which is slow on
Atom along with other SIMD multiplies.

Drop TBM detection; it'll probably never be useful for x264.

Invert FastShuffle to SlowShuffle; it only ever applied to one CPU (Conroe).

Detect CMOV, to fail more gracefully when run on a chip with MMX2 but no CMOV.
draft: x86_64 CABAC RDO asm
Fix some store forwarding stalls
There's quite a few others, but most of them don't help to fix or there's no
easy way to avoid them.
refine_subpel:kill some branches