arm64: dts: Update NAND MTD partition for Agilex and Stratix 10

Change NAND flash MTD partition in device tree after implementation of
UBI and UBIFS. "u-boot" partition remain for raw u-boot image, but "root"
partition is use for UBI image containing all other components.

Signed-off-by: Sin Hui Kho <sin.hui.kho@intel.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>