freedreno/ir3: some more shader-db stats

Add some stats about # of instructions per instruction category. Ie. an change that reduced instruction count, but increased cat4 instructions, might be worse. Some of this we could indirectly see before in stats about # of (ss)/(sy) flags.

Pulled out of my https://gitlab.freedesktop.org/robclark/mesa/-/commits/wip/unpack-load-const branch, with the idea to land before !5810 (merged) so we could see if we were falling down to ldc too much in anything that matters.