KVM: arm64: Enable SCTLR2 when advertised to the guest

HCRX_EL2.SCTLR2En needs to be set for SCTLR2_EL1 to take effect in
hardware (in addition to disabling traps).

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250708172532.1699409-14-oliver.upton@linux.dev


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