85xx: enable the auto self refresh for wake up ARP

The wake up ARP feature need use the memory to process
wake up packet, we enable auto self refresh to support it.

Signed-off-by: Dave Liu <daveliu@freescale.com>
Acked-by: Andy Fleming <afleming@freescale.com>

board/freescale/mpc8536ds/ddr.c

@@ -79,4 +79,10 @@ void fsl_ddr_board_options(memctl_options_t *popts,
 	 *	- number of DIMMs installed
 	 */
 	popts->half_strength_driver_enable = 0;
+
+	/*
+	 * For wake up arp feature, we need enable auto self refresh
+	 */
+	popts->auto_self_refresh_en = 1;
+	popts->sr_it = 0x6;
 }