arm64: KVM: Convert __cpu_reset_hyp_mode to using __hyp_reset_vectors

We are now able to use the hyp stub to reset HYP mode. Time to
kiss __kvm_hyp_reset goodbye, and use __hyp_reset_vectors.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>