KVM: arm64: Make RVBAR_EL2 accesses UNDEF

KVM: arm64: Make RVBAR_EL2 accesses UNDEF

We always expose a virtual CPU that has EL3 when NV is enabled,
irrespective of EL3 being actually implemented in HW.

Therefore, as per the architecture, RVBAR_EL2 must UNDEF, since
EL2 is not the highest implemented exception level. This is
consistent with RMR_EL2 also triggering an UNDEF.

Adjust the handling of RVBAR_EL2 accordingly.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250714122634.3334816-2-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>