ANDROID: KVM: arm64: Track the SVE state in the hypervisor vcpu structure

When dealing with a guest with SVE enabled, make sure the host SVE
state is pinned at EL2 S1, and that the hypervisor vCPU state is
correctly initialised (and then unpinned on teardown).

Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 233587962
Change-Id: Ic4d0ef9a6124701026cd56f6725ab4737857ed5b