panfrost/midgard: Merge embedded constants

panfrost/midgard: Merge embedded constants

In Midgard, a bundle consists of a few ALU instructions. Within the
bundle, there is room for an optional 128-bit constant; this constant is
shared across all instructions in the bundle.

Unfortunately, many instructions want a 128-bit constant all to
themselves (how selfish!). If we run out of space for constants in a
bundle, the bundle has to be broken up, incurring a performance and
space penalty.

As an optimization, the scheduler now analyzes the constants coming in
per-instruction and attempts to merge shared components, adjusting the
swizzle accessing the bundle's constants appropriately. Concretely,
given the GLSL:

   (a * vec4(1.5, 0.5, 0.5, 1.0)) + vec4(1.0, 2.3, 2.3, 0.5)

instead of compiling to the naive two bundles:

   vmul.fmul [temp], [a], r26
   fconstants 1.5, 0.5, 0.5, 1.0

   vadd.fadd [out], [temp], r26
   fconstants 1.0, 2.3, 2.3, 0.5

The scheduler can now fuse into a single (pipelined!) bundle:

   vmul.fmul [temp], [a], r26.xyyz
   vadd.fadd [out], [temp], r26.zwwy
   fconstants 1.5, 0.5, 1.0, 2.3

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