intel/fs: Constant propagate into SHADER_OPCODE_SHUFFLE

Code already exists to convert SHADER_OPCODE_SHUFFLE into a simple MOV
when either source is constant. However... the constants have to
actually get into those sources!

On a shader that I'm working on that multiplies very large matrices using
lots of subgroup operations,

-SIMD8 shader: 1378 instructions. 3 loops. 793896 cycles. 0:0 spills:fills, 23 sends, scheduled with mode non-lifo. Promoted 0 constants. Compacted 22048 to 21664 bytes (2%)
+SIMD8 shader: 346 instructions. 3 loops. 61742 cycles. 0:0 spills:fills, 23 sends, scheduled with mode top-down. Promoted 0 constants. Compacted 5536 to 5216 bytes (6%)

No changes in shader-db or fossil-db on any Intel platform.

v2: Merge a bunch of identical cases. Suggested by Ken.

Reviewed-by: Caio Oliveira <caio.oliveira@intel.com> [v1]
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23609>

src/intel/compiler/brw_fs_copy_propagation.cpp

@@ -1086,23 +1086,12 @@ fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
       case SHADER_OPCODE_TYPED_SURFACE_WRITE_LOGICAL:
       case SHADER_OPCODE_BYTE_SCATTERED_WRITE_LOGICAL:
       case SHADER_OPCODE_BYTE_SCATTERED_READ_LOGICAL:
-         inst->src[i] = val;
-         progress = true;
-         break;
-
       case FS_OPCODE_UNIFORM_PULL_CONSTANT_LOAD:
       case SHADER_OPCODE_BROADCAST:
-         inst->src[i] = val;
-         progress = true;
-         break;
-
       case BRW_OPCODE_MAD:
       case BRW_OPCODE_LRP:
-         inst->src[i] = val;
-         progress = true;
-         break;
-
       case FS_OPCODE_PACK_HALF_2x16_SPLIT:
+      case SHADER_OPCODE_SHUFFLE:
          inst->src[i] = val;
          progress = true;
          break;