cb4x4: Move sub-4X4 TX sizes behind CONFIG_CHROMA_2X2.

cb4x4 itself should not require these sizes.

This simplifies compatibility with other experiments, since we can
first make them work with cb4x4 (which is now on by default), and
then worry about chroma_2x2 (which is not) in separate steps.

Encoder and decoder output should remain unchanged.

Change-Id: I4e9fcdae49f238b5099a3c74a398fe993c2545f8
diff --git a/av1/common/idct.c b/av1/common/idct.c
index d12c3be..e94598e 100644
--- a/av1/common/idct.c
+++ b/av1/common/idct.c
@@ -1295,7 +1295,7 @@
 }
 #endif  // CONFIG_TX64X64
 
-#if CONFIG_CB4X4
+#if CONFIG_CHROMA_2X2
 static void inv_txfm_add_2x2(const tran_low_t *input, uint8_t *dest, int stride,
                              int eob, TX_TYPE tx_type, int lossless) {
   tran_high_t a1 = input[0] >> UNIT_QUANT_SHIFT;
@@ -2465,7 +2465,7 @@
     aom_highbd_iwht4x4_1_add(input, dest, stride, bd);
 }
 
-#if CONFIG_CB4X4
+#if CONFIG_CHROMA_2X2
 static void highbd_inv_txfm_add_2x2(const tran_low_t *input, uint8_t *dest,
                                     int stride, int eob, int bd,
                                     TX_TYPE tx_type, int lossless) {
@@ -2778,7 +2778,7 @@
       // case.
       inv_txfm_add_4x4(input, dest, stride, eob, tx_type, lossless);
       break;
-#if CONFIG_CB4X4
+#if CONFIG_CHROMA_2X2
     case TX_2X2:
       inv_txfm_add_2x2(input, dest, stride, eob, tx_type, lossless);
       break;
@@ -2908,7 +2908,7 @@
       av1_highbd_inv_txfm_add_4x4(input, dest, stride, eob, bd, tx_type,
                                   lossless);
       break;
-#if CONFIG_CB4X4
+#if CONFIG_CHROMA_2X2
     case TX_2X2:
       highbd_inv_txfm_add_2x2(input, dest, stride, eob, bd, tx_type, lossless);
       break;