KVM: arm64: selftests: Add SCTLR2_EL1 to get-reg-list

Handle SCTLR2_EL1 specially as it is only visible to userspace when
FEAT_SCTLR2 is implemented for the VM.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250708172532.1699409-27-oliver.upton@linux.dev


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