KVM: arm64: Reintroduce __sve_save_state

Now that the hypervisor is handling the host sve state in
protected mode, it needs to be able to save it.

This reverts commit e66425fc ("KVM: arm64: Remove unused
__sve_save_state").

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://lore.kernel.org/r/20240603122852.3923848-2-tabba@google.com


Signed-off-by: Marc Zyngier <maz@kernel.org>