Port SkTextureCompression opts to SkOpts

Port SkTextureCompression opts to SkOpts

Pretty vanilla translation.  I cleaned up who calls whom a little.
Used to be utils -> opts -> utils, now it's just utils -> opts.

I may follow up with a pass over the NEON code for readability
and to clean up dead code.

This turns on NEON A8->R11EAC conversion for ARMv8.
Unit tests which now hit the NEON code still pass.
I can't find any related bench.

BUG=skia:4117

Review URL: https://codereview.chromium.org/1273103002