imx6: fix random hang when download by usb

ROM did not invalidate L1 cache when download by usb
Need invalidate L1 cache before enable cache

Signed-off-by: Huang yongcai <b20788@freescale.com>
Signed-off-by: Frank Li <Frank.Li@freescale.com>

arch/arm/cpu/armv7/mx6/soc.c

@@ -150,6 +150,8 @@ int arch_cpu_init(void)
 #ifndef CONFIG_SYS_DCACHE_OFF
 void enable_caches(void)
 {
+	/* Avoid random hang when download by usb */
+	invalidate_dcache_all();
 	/* Enable D-cache. I-cache is already enabled in start.S */
 	dcache_enable();
 }