WindCharger: Flush data cache to memory before system restart.

This change flushes all printk messages from data cache to memory just
before the system is restarted for improved PRINTK_PERSIST buffer
consistency.

Change-Id: Ibd1f997592776b9dbeb3b3d6ecff021c831a1e82
diff --git a/arch/mips/ath79/setup.c b/arch/mips/ath79/setup.c
index 3c40b13..a990e85 100644
--- a/arch/mips/ath79/setup.c
+++ b/arch/mips/ath79/setup.c
@@ -39,6 +39,7 @@
 
 static void ath79_restart(char *command)
 {
+	dma_cache_wback_inv(0, ~0);
 	ath79_device_reset_set(AR71XX_RESET_FULL_CHIP);
 	for (;;)
 		if (cpu_wait)