ANDROID: KVM: arm64: Reset primary vCPU according to PVM firmware boot protocol

When a PVM firmware image is present for a protected VM, treat the first
running vCPU as the "primary" vCPU and reset its registers accordingly,
in particular by initialising its PC to enter the firmware at startup.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 254819795
Change-Id: I26676637145c7d809c5dc5ac0ad0e1fadaf275d2
Signed-off-by: Quentin Perret <qperret@google.com>