KVM: arm64: CSSELR_EL1 max is 13

Not counting TnD, which KVM doesn't currently consider, CSSELR_EL1
can have a maximum value of 0b1101 (13), which corresponds to an
instruction cache at level 7. With CSSELR_MAX set to 12 we can
only select up to cache level 6. Change it to 14.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201126134641.35231-2-drjones@redhat.com