radv/aco: enable 8/16-bit storage and int8/int16 on GFX8+

With this, Doom Eternal should now run with ACO on GFX8+.

The generated 8/16-bit storage code is okay but the generated int8/int16
code is currently pretty bad but it works and apparently Doom Eternal
doesn't actually use it (even though it requires it).

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <mesa/mesa!4707>
24 jobs for !4707 with aco_enable_8bit_16bit in 8 minutes and 52 seconds (queued for 3 seconds)
merge request