powerpc/mpc8xxx: Add memory reset control

JEDEC spec requires the clocks to be stable before deasserting reset
signal for RDIMMs. Clocks start when any chip select is enabled and
clock control register is set. This patch also adds the interface to
toggle memory reset signal if needed by the boards.

Signed-off-by: York Sun <yorksun@freescale.com>

include/configs/T4240QDS.h

@@ -161,6 +161,7 @@ unsigned long get_board_ddr_clk(void);
 #define QIXIS_LBMAP_DFLTBANK		0x00
 #define QIXIS_LBMAP_ALTBANK		0x04
 #define QIXIS_RST_CTL_RESET		0x83
+#define QIXIS_RST_FORCE_MEM		0x1
 #define QIXIS_RCFG_CTL_RECONFIG_IDLE	0x20
 #define QIXIS_RCFG_CTL_RECONFIG_START	0x21
 #define QIXIS_RCFG_CTL_WATCHDOG_ENBLE	0x08