mesa: add GL_UNSIGNED_INT_24_8 to _mesa_pack_depth_span
mesa: add GL_UNSIGNED_INT_24_8 to _mesa_pack_depth_span

Patch adds missing type (used with NV_read_depth) so that it gets
handled correctly. This fixes errors seen with following CTS test:

   ES3-CTS.gtf.GL3Tests.packed_pixels.packed_pixels

Signed-off-by: Tapani Pälli <cdcb67a5e49297de94340ca09f25994bd5e7f762@intel.com>
Reviewed-by: Iago Toral Quiroga <a847aabaac44184372f6b1cd1a59aa254daaeb0b@igalia.com>
Cc: "11.0" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler