pan/midgard: Validate tags when branching

pan/midgard: Validate tags when branching

Midgard prefetches instructions based on tag (ALU, LD/ST, texture *
size). To do so, the shader descriptor specifies the tag of the first
instruction, all instructions specify the tag of the next linear
instruction is, and all branches explicitly specify the tag of the
branch target.

If you mess this up, you get an INSTR_TYPE_MISMATCH, which unambiguously
refers to this problem, but it's still annoying to try to work out all
the branch targets in your head to debug.

Instead, let's track the tags of various blocks over time, so we can
automatically validate tags of branch targets, to make
INSTR_TYPE_MISMATCH issues immediately obvious in a disassembly.

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