AOM_QM: Use 8-bit matrices and fix 2x2 transform sizes.

2x2 transforms are now hidden behind the CHROMA_2X2 macro,
not the CB4X4 macro.

Change-Id: I5d73c679fba486ccda98fa8dbb804a3902df6c8d
diff --git a/aom_dsp/aom_dsp_common.h b/aom_dsp/aom_dsp_common.h
index 82f9a95..d879ec0 100644
--- a/aom_dsp/aom_dsp_common.h
+++ b/aom_dsp/aom_dsp_common.h
@@ -63,7 +63,7 @@
 
 #if CONFIG_AOM_QM
 typedef uint16_t qm_val_t;
-#define AOM_QM_BITS 6
+#define AOM_QM_BITS 5
 #endif
 #if CONFIG_HIGHBITDEPTH
 // Note: