Driver/DDR: Add Freescale DDR driver for ARM

Make PowerPC specific code conditional so ARM SoCs can reuse
this driver. Add DDR3 driver for ARM.

Signed-off-by: York Sun <yorksun@freescale.com>
diff --git a/README b/README
index 49f4b3a..d6006f5 100644
--- a/README
+++ b/README
@@ -450,6 +450,9 @@
 		CONFIG_SYS_FSL_DDRC_GEN3
 		Freescale DDR3 controller.
 
+		CONFIG_SYS_FSL_DDRC_ARM_GEN3
+		Freescale DDR3 controller for ARM-based SoCs.
+
 		CONFIG_SYS_FSL_DDR1
 		Board config to use DDR1. It can be enabled for SoCs with
 		Freescale DDR1 or DDR2 controllers, depending on the board