UPSTREAM: arm64: KVM: Implement 32bit system register save/restore

Implement the 32bit system register save/restore as a direct
translation of the assembly code version.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
(cherry picked from commit c209ec85)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>