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>
diff --git a/arch/powerpc/cpu/mpc85xx/ddr-gen1.c b/arch/powerpc/cpu/mpc85xx/ddr-gen1.c
index 8a86819..4dd8c0b 100644
--- a/arch/powerpc/cpu/mpc85xx/ddr-gen1.c
+++ b/arch/powerpc/cpu/mpc85xx/ddr-gen1.c
@@ -15,7 +15,7 @@
 #endif
 
 void fsl_ddr_set_memctl_regs(const fsl_ddr_cfg_regs_t *regs,
-			     unsigned int ctrl_num)
+			     unsigned int ctrl_num, int step)
 {
 	unsigned int i;
 	volatile ccsr_ddr_t *ddr = (void *)CONFIG_SYS_MPC8xxx_DDR_ADDR;