MA-11362 [Android] Update AVB lib in u-boot

MA-11362 [Android] Update AVB lib in u-boot

This commit did:
1. Sync the AVB lib with external/avb with commit head:
   commit 8a8103513dea5c47037200beabad2a307f09ecc8
   Merge: 2ee8dbe 852858e
   Author: David Zeuthen <zeuthen@google.com>
   Date:   Fri Jun 30 16:08:03 2017 +0000
   	Revert "avbtool: Avoid using $(ANDROID_VERITY_MODE) for now."
	am: 1b2f7a64e2
	am: 852858e2ed
2. Fix build error and implement ops function
   fsl_get_size_of_partition().

Change-Id: I3d1a04c320b8ea89e9fe28124cf866bd62282e78
Signed-off-by: Luo Ji <ji.luo@nxp.com>