st: Choose a 2101010 format for GL_RGB/GL_RGBA with a 2_10_10_10 type.

st: Choose a 2101010 format for GL_RGB/GL_RGBA with a 2_10_10_10 type.

GLES's GL_EXT_texture_type_2_10_10_10_REV allows uploading this type to an
unsized internalformat, and it should be non-color-renderable.
fbobject.c's implementation of the check for color-renderable is checks
that the texture has a 2101010 mesa format, so make sure that we have
chosen a 2101010 format so that check can do what it meant to.

Fixes KHR-GLES3.packed_pixels.pbo_rectangle.rgb on vc5.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>