intel/fs: Implement nir_intrinsic_load_global_constant

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6379>
diff --git a/src/intel/compiler/brw_fs_nir.cpp b/src/intel/compiler/brw_fs_nir.cpp
index 857ee8e..99cb0e7 100644
--- a/src/intel/compiler/brw_fs_nir.cpp
+++ b/src/intel/compiler/brw_fs_nir.cpp
@@ -4554,7 +4554,8 @@
       break;
    }
 
-   case nir_intrinsic_load_global: {
+   case nir_intrinsic_load_global:
+   case nir_intrinsic_load_global_constant: {
       assert(devinfo->gen >= 8);
 
       assert(nir_dest_bit_size(instr->dest) <= 32);