st/mesa: convert sub image for cube map arrays to 2d arrays for upload

st/mesa: convert sub image for cube map arrays to 2d arrays for upload

Since we can subimage upload a number of cube map array layers,
that aren't a complete cube map array, we should specify things
as a 2D array and blit from that.

Suggested by Ilia Mirkin as an alternate fix for texsubimage
cube map array issues.

seems to work just as well.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>