[qsd8650a_st1x] With USB connection force device into fastboot mode.

With this change during bootup, if USB is connected to the device then LK goes into
fastboot mode, no matter if boot.img is preset or not.

Minor code cleanup in aboot.c

Change-Id: I3a074321ec3802f5518f42b3b27d4d45c0577905
3 files changed