i965/skl: Align compressed textures to four times the block size

i965/skl: Align compressed textures to four times the block size

On Skylake it is possible to choose your own alignment values for
compressed textures but they are expressed as a multiple of the block
size. The minimum alignment value we can use is 4 so we effectively
have to align to 4 times the block size. This patch makes it initially
set mt->align_[wh] to the large alignment value and then later divides
it by the block size so that it can be uploaded as part of the surface
state.

Reviewed-by: Ben Widawsky <ben@bwidawsk.net>