ANDROID: KVM: arm64: Use 32-bit function ID for PSCI MEM_PROTECT call

The PSCI specification defines only a 32-bit function ID for the
MEM_PROTECT call used to protect against cold reboot attacks.

Fix the pKVM hypervisor invocation of MEM_PROTECT to use the 32-bit
function ID instead of the unallocated 64-bit flavour.

Bug: 260316363
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: I675a57419064f7f006960ca5370e9dc2d5279a90