texcompress_s3tc/fxt1: fix stride checks (v1.1)

texcompress_s3tc/fxt1: fix stride checks (v1.1)

The fastpath currently checks the RowLength != width, but
if you have a RowLength of 7, and Alignment of 4, then
that shouldn't match.

align the rowlength to the pack alignment before comparing.

This fixes compressed cases in CTS packed_pixels_pixelstore
test when SKIP_PIXELS is enabled, which causes row length
to get set.

v1.1: add fxt1 fix (Iago)

Cc: "11.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>