am33xx: Enable D-CACHE on !CONFIG_SYS_DCACHE_OFF

Test on Beaglebone white over cpsw, usb ether and SD card (read and
write), performance increased, crc32 of data matches.

Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/arch/arm/cpu/armv7/am33xx/board.c b/arch/arm/cpu/armv7/am33xx/board.c
index 803aa9c..c7dad66 100644
--- a/arch/arm/cpu/armv7/am33xx/board.c
+++ b/arch/arm/cpu/armv7/am33xx/board.c
@@ -241,3 +241,11 @@
 	sdram_init();
 #endif
 }
+
+#ifndef CONFIG_SYS_DCACHE_OFF
+void enable_caches(void)
+{
+	/* Enable D-cache. I-cache is already enabled in start.S */
+	dcache_enable();
+}
+#endif /* !CONFIG_SYS_DCACHE_OFF */