In order not to cause ABI regression, let's invent a new
androidboot.mode for NVMe instead. Just elaborate a bit more
that we now doesn't support mtd devices, otherwise we should
rework it to make it more scalable.
Change-Id: I115ffd0e5c4986f2e76fcbcf6700c31f297f7950
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>