platform: msm_shared: use mmc groups erase to perform "fastboot erase"

Erasing one block of MMC partition will leave garbage information.
The mmc groups erase will erase the partition clean. MMC blocks not aligned
with the mmc erase unit should be handled as special case.

CRs-Fixed: 500724
Change-Id: Ic735612e9d22b199a8c494079fc626814ac8fcc7
2 files changed