mesa: add fbo/texture support for ARB_texture_cube_map_array (v2)

mesa: add fbo/texture support for ARB_texture_cube_map_array (v2)

This adds the mesa core + texture + fbo support for the
texture cube map array extension.

v2:
add comment to _mesa_num_tex_faces related to cube map arrays (Brian)
drop wrong comment cut-n-paste (Brian)
fix / 6 maximum check issue (Kenneth)
coalsece some array case statements (Kenneth)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>