panfrost/midgard: Extend RA to non-vec4 sources

panfrost/midgard: Extend RA to non-vec4 sources

This represents a major break with the former RA design. We now use
conflicting register classes to represent the subdivision of Midgard's
128-bit registers into varying sizes and arrangement. We determine class
based on the number of components in the instructions' masks. To support
this, we include a number of helpers in the RA to allow composing
swizzles and masks, such that MIR written implicitly assuming .xyzw
sources can be transformed to use actual (non-aligned) sources.

The net result is a marked decrease in register pressure on
non-vec4-exclusive shaders. We could still be doing much better. Not
implemented yet are:

   - Register spilling
   - Per-component liveness

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Ryan Houdek <Sonicadvance1@gmail.com>