To boot UniPhier boards with the NAND boot mode, two images
(u-boot-spl.bin and u-boot-dtb.img) must be written at the correct
offset addresses.
TFTP downloading is useful to update such images in the NAND device.
We generally do:
  => nand erase 0 0x100000
  => tftpboot u-boot-spl.bin
  => nand write $loadaddr 0 0x10000
  => tftpboot u-boot-dtb.img
  => nand write $loadaddr 0x10000 0xf0000
It is a tedious and error-prone operation.
This commit provides the shorthand:
  => run nandupdate
Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
        "image_offset=0x00080000\0"             \
        "image_size=0x00f00000\0"               \
        "verify=n\0"                            \
+       "nandupdate=nand erase 0 0x100000 &&"                           \
+                  "tftpboot u-boot-spl.bin &&"                         \
+                  "nand write $loadaddr 0 0x10000 &&"                  \
+                  "tftpboot u-boot-dtb.img &&"                         \
+                  "nand write $loadaddr 0x10000 0xf0000\0"             \
        "norboot=run add_default_bootargs &&"                           \
                "bootm $image_offset\0"                                 \
        "nandboot=run add_default_bootargs &&"                          \