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

KVM: arm64: Track 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).

Co-authored-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20250416152648.2982950-2-qperret@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>