intel/fs: Choose memory message type based on bit size

intel/fs: Choose memory message type based on bit size

Thanks to the NIR vectorizing pass, we're about to see alignments that
are higher than the bit size.  Previously, we could use either and we
just happened to choose alignment (probably the wrong choice) so it's
harmless to switch to detecting based on bit size.  This commit changes
things to take both into account which is more accurate to what the
messages we're using do.  We also beef up the asserts and make them more
consistent, more accurate, and more complete.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4367>