ENGR00209059 android: refine fastboot and recovery support.

1. add check asrc register to enter recovery mode,
   rather then check the file.
2. fix the boot.img can not fastboot flash function.
3. consolidate and cleanup fastboot code.
4. clean up many build warnning message.

Signed-off-by: Zhang Jiejing <jiejing.zhang@freescale.com>