i965/vec4: Handle component qualifiers on non-generic varyings.

i965/vec4: Handle component qualifiers on non-generic varyings.

ARB_enhanced_layouts only requires component qualifier support for
generic varyings, so this is all the vec4 backend knew how to handle.

This patch extends the backend to handle it for all varyings, so we
can use store_output intrinsics with a component set for things like
clip/cull distances.  We may want to use that for other VUE header
fields in the future as well.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>