st/mesa: align cube map arrays layers

st/mesa: align cube map arrays layers

We create textures internally for texsubimage, and we use
the values from sub image to create a new texture, however
we don't align these to valid sizes, and cube map arrays
must have an array size aligned to 6.

This fixes texsubimage cube_map_array on CAYMAN at least,
(it was causing  GPU hang and bad values), it probably
also fixes it on radeonsi and evergreen.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89957
Tested-by: Tom Stellard <thomas.stellard@amd.com>
Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>