panfrost/midgard: Add integer outmods

panfrost/midgard: Add integer outmods

For floats, output modifiers determine clamping behaviour. For integers,
they determine wrapping/saturation behaviour (or shifting -- see next
commit). These are very different; they are conceptually two unrelated
enums union'ed together; the distinction is responsible for many-a-bug.
While clamping behaviour for floats was clear from GL, the int behaviour
is only known From OpenCL contortion with convert_*_sat() functions.

With the underlying functions known, clean up the codebase, likely
fixing outmod type related bugs in the process.

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