ppc4xx: Fixed offset of refresh rate type for Bamboo on-board DDR SDRAM

This patch also adds a note to the fixed DDR setup for Bamboo NAND booting:

Note:
As found out by Eugene O'Brien <eugene.obrien@advantechamt.com>, the fixed
DDR setup has problems (U-Boot crashes randomly upon TFTP), when the DIMM
modules are still plugged in. So it is recommended to remove the DIMM
modules while using the NAND booting code with the fixed SDRAM setup!

Signed-off-by: Eugene O'Brien <eugene.obrien@advantechamt.com>
Signed-off-by: Stefan Roese <sr@denx.de>

board/amcc/bamboo/bamboo.c

@@ -67,13 +67,13 @@ const unsigned char cfg_simulate_spd_eeprom[128] = {
 	0x00,    /* Module data width continued: +0 */
 	0x04,    /* 2.5 Volt */
 	0x75,    /* SDRAM Cycle Time (cas latency 2.5) = 7.5 ns */
+	0x00,    /* SDRAM Access from clock */
 #ifdef CONFIG_DDR_ECC
 	0x02,    /* ECC ON : 02 OFF : 00 */
 #else
 	0x00,    /* ECC ON : 02 OFF : 00 */
 #endif
-	0x82,    /* refresh Rate Type: Normal (15.625us) + Self refresh */
-	0,
+	0x82,    /* refresh Rate Type: Normal (7.8us) + Self refresh */
 	0,
 	0,
 	0x01,    /* wcsbc = 1 */

nand_spl/board/amcc/bamboo/sdram.c

@@ -44,6 +44,12 @@ static void wait_init_complete(void)
  * not enough free space to implement the complete I2C SPD DDR autodetection
  * routines. Therefore the Bamboo only supports the onboard 64MBytes of SDRAM
  * when booting from NAND flash.
+ *
+ * Note:
+ * As found out by Eugene O'Brien <eugene.obrien@advantechamt.com>, the fixed
+ * DDR setup has problems (U-Boot crashes randomly upon TFTP), when the DIMM
+ * modules are still plugged in. So it is recommended to remove the DIMM
+ * modules while using the NAND booting code with the fixed SDRAM setup!
  */
 void early_sdram_init(void)
 {