anv: fix color write enable interaction with color mask

anv: fix color write enable interaction with color mask

Color writes & color masks occupy the same fields in the BLEND_STATE
structure. So we need to store color mask (which are not dynamic) on
the pipeline to merge that information with color writes.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: b15bfe92f7f8 ("anv: implement VK_EXT_color_write_enable")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/6111
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15310>