KVM: arm64: Export kvm_are_all_memslots_empty()

Export kvm_are_all_memslots_empty(). This will be used by a future
commit when checking before setting a capability.

Signed-off-by: Ricardo Koller <ricarkol@google.com>
Reviewed-by: Shaoqin Huang <shahuang@redhat.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Link: https://lore.kernel.org/r/20230426172330.1439644-5-ricarkol@google.com


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>