ARM: dts: imx: ocram size is different between imx6q and imx6dl

The ocram on imx6q is 256 KiB while on imx6dl it's 128 KiB.  Let's
have separate node for imx6q and imx6dl.  It also changes imx6q size
0x3f000 to 0x40000 to match the hardware.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Liu Ying <Ying.Liu@freescale.com>