i965: expose MESA_FORMAT_B8G8R8X8_SRGB visual

i965: expose MESA_FORMAT_B8G8R8X8_SRGB visual

Patch adds BGRX sRGB visuals, required format translation information
to the __DRI_IMAGE_FOURCC_SXRGB8888 format and makes all BGRX visuals
sRGB capable just like is done with BGRA.

squashed patches from Yevhenii Kolesnikov:
  dri: Add __DRI_IMAGE_FOURCC_SXRGB8888 conversion
  i965: force visuals without alpha bits to use sRGB

Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/1501
Cc: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Signed-off-by: Yevhenii Kolesnikov <yevhenii.kolesnikov@globallogic.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3077>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3077>