KVM: arm64: Relax invariance of KVM_ARM_VCPU_POWER_OFF

Allow the value of KVM_ARM_VCPU_POWER_OFF to differ between calls to
KVM_ARM_VCPU_INIT. Userspace can already change the state of the vCPU
through the KVM_SET_MP_STATE ioctl, so making the bit invariant seems
needlessly restrictive.

Link: https://lore.kernel.org/r/20230609190054.1542113-3-oliver.upton@linux.dev


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>