UPSTREAM: arm64: KVM: HYP mode entry points

Add the entry points for HYP mode (both for hypercalls and
exception handling).

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
(cherry picked from commit 2b28162c)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>