softmmu/memory: Pass ram_flags to memory_region_init_ram_shared_nomigrate()

Let's forward ram_flags instead, renaming
memory_region_init_ram_shared_nomigrate() into
memory_region_init_ram_flags_nomigrate().

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Acked-by: Eduardo Habkost <ehabkost@redhat.com> for memory backend and machine core
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210510114328.21835-6-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>