Eliminate static initializers in SkColor_SSE2.h.

Eliminate static initializers in SkColor_SSE2.h.

Chrome hates static initializers.

Two global masks can become a single local mask instead.  Perf looks like a no-op:

$ c --match bitmaprect_80 bitmap_RGBA --config 8888
                              bitmap_RGBA_8888_scale	13.7us -> 14.1us	1.03x
                    bitmap_RGBA_8888_update_volatile	4.53us ->  4.6us	1.02x
                                    bitmap_RGBA_8888	4.55us -> 4.61us	1.01x
                             bitmap_RGBA_8888_update	4.64us -> 4.67us	1.01x
             bitmap_RGBA_8888_A_source_stripes_three	9.66us -> 9.71us	1.01x
                       bitmaprect_80_filter_identity	10.6us -> 10.5us	0.99x
                     bitmaprect_80_nofilter_identity	10.5us -> 10.4us	0.99x

TBR=reed@google.com
BUG=skia:

Review URL: https://codereview.chromium.org/762453002