arm64: KVM: Rename HCR_VA to HCR_VSE

HCR_VA is a leftover from ARMv7, On ARMv8, this is HCR_VSE
(which stands for Virtual System Error), and has better
defined semantics.

Let's rename the constant.

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