KVM: arm64: nv: Allow userspace to set PSR_MODE_EL2x

KVM: arm64: nv: Allow userspace to set PSR_MODE_EL2x

We were not allowing userspace to set a more privileged mode for the VCPU
than EL1, but we should allow this when nested virtualization is enabled
for the VCPU.

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230209175820.1939006-6-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>