KVM: arm64: Disable privileged hypercalls after pKVM finalisation

After pKVM has been 'finalised' using the __pkvm_prot_finalize hypercall,
the calling CPU will have a Stage-2 translation enabled to prevent access
to memory pages owned by EL2.

Although this forms a significant part of the process to deprivilege the
host kernel, we also need to ensure that the hypercall interface is
reduced so that the EL2 code cannot, for example, be re-initialised using
a new set of vectors.

Re-order the hypercalls so that only a suffix remains available after
finalisation of pKVM.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211008135839.1193-7-will@kernel.org