[Mesa-dev] [rfc] radv: move user sgpr to compiler side

[Dave Airlie]

On radeonsi hw we have 16 user defined sgprs we can use to feed
32-bit constant values to the shader, we've up until now statically
partitioned these, but this can be limiting going forward and also
leads to having unused sgprs.

Also radv has currently a limit of 4 descriptor sets, to raise that
above that we need to switch to a better allocation scheme (this
patchset doesn't do that yet).

The first few patches are just moving code around, and moving 
descriptor emission to the draw flushing code. The main patches
are 8, 9, 10. 8 introduces a new interface between radv and ac
code to encapsulate the user sgprs for the state setting code
to look then up. 9 reworks the descriptor sets we have now, so
we only emit them if the layout we are bound with requires them,
and 10 makes the push constant binding optional on whether it is used.

It should be possible to make the PS sample position and CS grid size,
ones optional, however NIR lacks a scanning pass like TGSI, so I'd have
to enhance things to know earlier what intrinsics are used. I suppose
it might make sense in the future to push this into LLVM for some things.

Dave.