imx: mx6dlarm2: Add support for i.MX6DL arm2 DDR3 board

imx: mx6dlarm2: Add support for i.MX6DL arm2 DDR3 board

This patch adds the i.MX6DL arm2 board support. The i.MX6DL ARM2
shared the same board with i.MX6Q ARM2 board since the i.MX6DL is
pin-pin compatible with i.MX6Q.

The patch also support the DDR 32-BIT mode option. Please define
CONFIG_DDR_32BIT in the board configure file to enable DDR 32-BIT
mode.But due to the board design, it's 64bit DDR buswidth physically,
so, if you CONFIG_DDR_32BIT, the DDR memory size will be half of it.

Signed-off-by: Ye.Li <B37916@freescale.com>