Approach to update kboot/kernel/rootfs

[matt_hsu]

Hi Andy,

I tried the your patches for kboot on GTA03_EVB. It seems to work.
But here comes an issue, that's, how to program kboot/kernel/rootfs on
kboot?
Previously, we use DFU to upgrade everything. One solution is to add the
support of DFU in kboot.
Then use a key-pressing signal (like AUX key) to let switch DFU mode.

Anyway, we need a easy approach to let HW people to replace kernel/rootfs.

Cheers,

Matt