i965: Micro-optimize swizzle_to_scs() and make it inlinable.

i965: Micro-optimize swizzle_to_scs() and make it inlinable.

brw_swizzle_to_scs has been showing up in my CPU profiling, which is
rather silly - it's a tiny amount of code.  It really should be inlined,
and can easily be implemented with fewer instructions.

The enum translation is as follows:

SWIZZLE_X, SWIZZLE_Y, SWIZZLE_Z, SWIZZLE_W, SWIZZLE_ZERO, SWIZZLE_ONE
        0          1          2          3             4            5
        4          5          6          7             0            1
  SCS_RED, SCS_GREEN,  SCS_BLUE, SCS_ALPHA,     SCS_ZERO,     SCS_ONE

which is simply (swizzle + 4) & 7.

Haswell needs extra textureGather workarounds to remap GREEN to BLUE,
but Broadwell and later do not.

This patch replicates swizzle_to_scs in gen7_wm_surface_state.c and
gen8_surface_state.c, since the Gen8+ code can be simplified to a mere
two instructions.  Both copies can be marked static for easy inlining.

v2: Put the commit message in the code as comments (requested by
    Jason Ekstrand).  Also fix a typo.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>