i965: Override swizzles for integer luminance formats.

i965: Override swizzles for integer luminance formats.

The hardware's integer luminance formats are completely unusable;
currently we fall back to RGBA.  This means we need to override
the texture swizzle to obtain the XXX1 values expected for luminance
formats.

Fixes spec/EXT_texture_integer/texwrap formats bordercolor [swizzled]
on Broadwell - 100% of border color tests now pass on Broadwell.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Cc: mesa-stable@lists.freedesktop.org