arm: mvebu: spl: Fix support for loading U-Boot proper from SD card

Marvell BootROM loads MMC image from sector 0 (HW boot or data partition)
and SD image from sector 1.

So for SD card booting it is needed to not use constant CONFIG MMC options
and instead of them it is needed to define functions spl_mmc_boot_mode()
spl_mmc_get_uboot_raw_sector() which determinate offsets at SPL runtime
based on MMC or SD card.

Calculation of SD card sector expects following values:
CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_DATA_PART_OFFSET=0
CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0

Fixes: 2226ca17 ("arm: mvebu: Load U-Boot proper binary in SPL code based on kwbimage header")
Signed-off-by: Pali Rohár <pali@kernel.org>