gallium: add FMA and DFMA opcodes (v3)

Needed by ARB_gpu_shader5.

v2: select DMAD for FMA with double precision
v3: add and select DFMA

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
diff --git a/src/gallium/drivers/nouveau/nv50/nv50_screen.c b/src/gallium/drivers/nouveau/nv50/nv50_screen.c
index ed07ba4..829dfbc 100644
--- a/src/gallium/drivers/nouveau/nv50/nv50_screen.c
+++ b/src/gallium/drivers/nouveau/nv50/nv50_screen.c
@@ -289,6 +289,7 @@
    case PIPE_SHADER_CAP_DOUBLES:
    case PIPE_SHADER_CAP_TGSI_DROUND_SUPPORTED:
    case PIPE_SHADER_CAP_TGSI_DFRACEXP_DLDEXP_SUPPORTED:
+   case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
       return 0;
    default:
       NOUVEAU_ERR("unknown PIPE_SHADER_CAP %d\n", param);