ARM: imx: add suspend in ocram support for i.mx6dl

i.MX6DL's suspend in ocram function is derived from i.MX6Q,
it can lower the DDR IO power from ~26mA@1.5V to ~15mA@1.5V,
measured on i.MX6DL SabreSD board, R25.

Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>