apm821xx: nand: add NVMEM-on-UBI support
Oversight from 8d302f5ebc6e2787d01d6c6a8ef6bcc403949705 , which requires
this to work. I couldn't test it as I ended up wiping my UBI volume by
accident.
Signed-off-by: Rosen Penev <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/16580
Signed-off-by: Robert Marko <[email protected]>