ARM: dts: imx: Fix eMMC boot on Data Modul i.MX8M Plus eDM SBC

In case the i.MX8M Plus starts from eMMC BOOT1/BOOT2 HW partitions, the
flash.bin container is stored at offset 0 from the start, that means the
fitImage itb is at offset 0x2c0 instead of 0x300 sectors from the start.
Handle this difference in custom spl_mmc_get_uboot_raw_sector() .

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>