Resume on Reboot default implementation

A default implementation of the RebootEscrow HAL which relies on RAM
retention to keep a key around during a reboot to apply an OTA. This
should work on devices that use a "warm reboot" and most likely will
work on devices that use a "cold reboot" as well.

DRAM will retain information for several seconds depending on the
temperature and other factors. This is enough to survive a reboot. With
the Hadamard code used in this change for error recovery, many errors
can be recovered.

Bug: 63928581
Test: make
Test: atest VtsHalRebootEscrowTargetTest
Change-Id: Ib8db7888d64fee8d827d7c06892b9a1f2af87add