anv: Don't use bogus alpha swizzles

anv: Don't use bogus alpha swizzles

For RGB formats in Vulkan, we use the corresponding RGBA format with a
swizzle of RGB1.  While this swizzle is exactly what we want for
texturing, it's not allowed for rendering according to the docs.  While
we haven't been getting hangs or anything, we should probably obey the
docs.  This commit just sanitizes all render swizzles so that the alpha
channel maps to ALPHA.

Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>