arm: mvebu: Add support for generating NAND kwbimage

arm: mvebu: Add support for generating NAND kwbimage

Add a new Kconfig option CONFIG_MVEBU_SPL_BOOT_DEVICE_NAND which instruct
make to generate kwbimage with NAND header. This image is used for booting
from NAND flash (either SPI or parallel).

Support is very simple, SPL after finishes DDR training returns back to the
BootROM (via CONFIG_SPL_BOOTROM_SUPPORT option) and BootROM then loads and
executes U-Boot proper.

To generate correct kwbimage NAND header, it is required to set following
Kconfig options:

CONFIG_SYS_NAND_PAGE_SIZE
CONFIG_SYS_NAND_BLOCK_SIZE
CONFIG_MVEBU_SPL_NAND_BADBLK_LOCATION

They are used only by make / mkimage when generating final kwbimage.

CONFIG_MVEBU_SPL_NAND_BADBLK_LOCATION is a new mvebu specific Kconfig
option which is set into kwbimage NAND_BADBLK_LOCATION header field.

Signed-off-by: Pali Rohár <pali@kernel.org>