i965: Make swizzle_to_scs non-static.

i965: Make swizzle_to_scs non-static.

We'll need this for Broadwell code as well.

Normally, when we make things public, we add the "brw" prefix.  I'm not
crazy about that in this case, since it deals with prog_instruction.h's
SWIZZLE_XYZW values, rather than the BRW_SWIZZLE_XYZW enums.  However,
I can't think of a better name, and at least the comments and code make
it clear.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Acked-by: Anuj Phogat <anuj.phogat@gmail.com>