add missing case statements for TGSI_TOKEN_TYPE_IMMEDIATE and assert(0)

We're hitting this with quite a few Mesa demos.

src/mesa/pipe/tgsi/exec/tgsi_sse2.c

@@ -2245,6 +2245,11 @@ tgsi_emit_sse2(
             &parse.FullToken.FullInstruction );
          break;
 
+      case TGSI_TOKEN_TYPE_IMMEDIATE:
+         /* XXX implement this */
+         assert(0);
+         break;
+
       default:
          assert( 0 );
       }
@@ -2321,6 +2326,11 @@ tgsi_emit_sse2_fs(
             &parse.FullToken.FullInstruction );
          break;
 
+      case TGSI_TOKEN_TYPE_IMMEDIATE:
+         /* XXX implement this */
+         assert(0);
+         break;
+
       default:
          assert( 0 );
       }