app: aboot: Modify erase size from 1 block to 4k

fastboot erase command only erase 1 block currently. But ext4's super
block is placed after 1k. So erase 1 block will make no sense. It also
fails when target is EFS. So modify the size from 1 block to 4k.

CRs-fixed: 526528
Change-Id: I0811e54be6aa74871e3862aa2d1c7067650227b8
1 file changed