mesa: Add GL_UNSIGNED_INT_2_10_10_10_REV OES read type for BGRX1010102.

mesa: Add GL_UNSIGNED_INT_2_10_10_10_REV OES read type for BGRX1010102.

As Marek noted, the GL_RGBA + GL_UNSIGNED_INT_2_10_10_10_REV type
combo is also good for readback of BGRX1010102 framebuffers, not
only for BGRA1010102 framebuffers for use with glReadPixels()
under GLES, so add it for the GL_IMPLEMENTATION_COLOR_READ_TYPE_OES
query.

Successfully tested on gallium r600 driver with a (quickly hacked
for RGBA 10 10 10 0) dEQP testcase
dEQP-EGL.functional.wide_color.window_1010102_colorspace_default.

Suggested-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>