ANDROID: KVM: arm64: Use PSCI MEM_PROTECT to zap guest pages on reset

If a malicious/compromised host issues a PSCI SYSTEM_RESET call in the
presence of guest-owned pages then the contents of those pages may be
susceptible to cold-reboot attacks.

Use the PSCI MEM_PROTECT call to ensure that volatile memory is wiped by
the firmware if a SYSTEM_RESET occurs while unpoisoned guest pages exist
in the system. Since this call does not offer protection for a "warm"
reset initiated by SYSTEM_RESET2, detect this case in the PSCI relay and
repaint the call to a standard SYSTEM_RESET instead.

Bug: 196204410
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: I5c3dd93bc83ebcd0b6cea2ec734f6e3a77f0064e