x86: faster AVX satd/sa8d/sa8d_satd/hadamard_ac

Use Conroe-style movddup in AVX transforms; both Sandy Bridge and Bulldozer
do movddup in the load unit, so it's totally free this way.

On Sandy Bridge:
~6% faster sa8d_satd
~5% faster hadamard_ac
~9% faster 32-bit satd
~2% faster sa8d
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.