v3d: add load_fep_w_v3d intrinsic

This intrinsic helps to read the W coordinate stored in the QPU register
when initializing the input data for the fragment shaders.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28072>

src/broadcom/compiler/nir_to_vir.c

@@ -3543,6 +3543,10 @@ ntq_emit_intrinsic(struct v3d_compile *c, nir_intrinsic_instr *instr)
                 vir_emit_tlb_color_read(c, instr);
                 break;
 
+        case nir_intrinsic_load_fep_w_v3d:
+                ntq_store_def(c, &instr->def, 0, vir_MOV(c, c->payload_w));
+                break;
+
         case nir_intrinsic_load_input:
                 ntq_emit_load_input(c, instr);
                 break;