anv: reduce push constant size for descriptor sets

Now that descriptor sets are located a in a 1Gb area, we can avoid
storing the whole address to the descriptor and add the base address
of the area to a 32bit offset.

Replay a bunch of fossils with this and changes not really significant
one way or another :

Totals:
Instrs: 9278246 -> 9277148 (-0.01%); split: -0.01%, +0.00%
Cycles: 3547598421 -> 3547579435 (-0.00%); split: -0.00%, +0.00%

Totals from 353 (1.14% of 31021) affected shaders:
Instrs: 581546 -> 580448 (-0.19%); split: -0.23%, +0.04%
Cycles: 25885422 -> 25866436 (-0.07%); split: -0.31%, +0.24%

No difference on send messages or spills/fills.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21645>

src/intel/compiler/brw_compiler.h

@@ -737,6 +737,7 @@ enum brw_shader_reloc_id {
    BRW_SHADER_RELOC_SHADER_START_OFFSET,
    BRW_SHADER_RELOC_RESUME_SBT_ADDR_LOW,
    BRW_SHADER_RELOC_RESUME_SBT_ADDR_HIGH,
+   BRW_SHADER_RELOC_DESCRIPTORS_ADDR_HIGH,
 };
 
 enum brw_shader_reloc_type {