app: aboot: Add AVB2.0 changes to aboot files

Incorporate AVB2.0 changes to aboot.Add function
to free boot resources and provide support for
custom_key validation required for yellow state
AVB 2.0 validation. Fix compilation issues for
AVB as well.

Change-Id: Ie196174028dd3dac04c58845fe09a75f055d3094
2 files changed