Add erase of whole eMMC command before flashing.

* LK bootloader does not erase partition before flashing.
Failing to erase the partition before flashing results in
the wrong data on the partition and causes unexpected failures
during mounting the rootfs and starting the mendel OS.

Change-Id: I5967940f788e28d04897e6b28463d9fb3e8bbe00
1 file changed