ARM: KVM: Switch the CP reg search to be a binary search

Doing a linear search is a bit silly when we can do a binary search.
Not that we trap that so many things that it has become a burden yet,
but it makes sense to align it with the arm64 code.

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>