This actually uses the EMMC partition access code. In order for this
to work, the BML partition name is changed back to the block
device name (e.g. "boot" -> "/dev/block/bml9"), and the
BML_UNLOCK_ALL ioctl is called before writing.
Change-Id: I012f1eca0b486b7465ca38b5db1f513ee8a246ea