panfrost/midgard: Disambiguate register mode

panfrost/midgard: Disambiguate register mode

We postfix instructions by their size if a destination override is in
place (a la AT&T assembly), disambiguating instruction sizes.
Previously, "16-bit instruction, 16-bit dest, 16-bit sources"
disassembled identically to "32-bit instruction, 16-bit dest, 16-bit
sources", which is semantically distinct due to the lessened opportunity
for parallelism but (potentially) greater precision. Adding a postfix
removes the ambiguity and relieves mental gymnastics reading weird
disassemblies even in some cases that are not ambiguous.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>