fastboot: Add support for fastboot flashing commands

Commands added:
fastboot flashing lock
      - Prevents flashing partitions
fastboot flashing unlock
      - Enable user to flashing partitions
fastboot flashing lock_critical
      - Prevents flashing bootloader related
        paritions
fastboot flashing unlock_critical
      - Enables user to flash bootloader
        related partitions
fastboot flashing get_unlock_ability
      - Query bootloader to check if device is
        locked.

(cherry picked from commit bf11095f)
Change-Id: Id6db16ba32f7a2b1c3f041a76bd3bdf2d3ab471e