[dev][nandpart][bad-block] Implement bad-block protocol.

bad-block protocol implementation is specific to the methodology used
in the AML u-boot bootloader. We preserve the same semantics so as to
allow the bootloader to continue to read the system partitions even
after additional bad blocks have been grown.

Change-Id: I37954fccf67822459f9c7522c0299a5568c65fb1
Tested: TODO