arm64: Don't enable VHE for the kernel if OVERRIDE_HVHE is set

arm64: Don't enable VHE for the kernel if OVERRIDE_HVHE is set

If the OVERRIDE_HVHE SW override is set (as a precursor of
the KVM_HVHE capability), do not enable VHE for the kernel
and drop to EL1 as if VHE was either disabled or unavailable.

Further changes will enable VHE at EL2 only, with the kernel
still running at EL1.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20230609162200.2024064-6-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>