Update the ddr scripts for LPDDR2 and add two build configs for LPDDR2 arm2 board. Since the LPDDR2 arm2 board has different DDR size, use CONFIG_DDR_MB in defconfig to replace the PHYS_SDRAM_SIZE.
Signed-off-by: Ye.Li
CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx6qarm2/imximage.cfg,MX6Q,MX6DQ_LPDDR2,DDR_MB=512" CONFIG_ARM=y CONFIG_TARGET_MX6QARM2=y
