i.MX28: Make use of the bounce buffer

This allows i.MX28 MMC host to fully utilize DMA transfers and caches, greatly
improving speed.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@gmail.com>

include/configs/m28evk.h

@@ -140,6 +140,7 @@
  */
 #ifdef	CONFIG_CMD_MMC
 #define	CONFIG_MMC
+#define	CONFIG_MMC_BOUNCE_BUFFER
 #define	CONFIG_GENERIC_MMC
 #define	CONFIG_MXS_MMC
 #endif

include/configs/mx28evk.h

@@ -138,6 +138,7 @@
 #ifdef	CONFIG_CMD_MMC
 #define CONFIG_MMC
 #define CONFIG_GENERIC_MMC
+#define CONFIG_MMC_BOUNCE_BUFFER
 #define CONFIG_MXS_MMC
 #endif