memory-device: Refactor memory_device_pre_plug()

memory-device: Refactor memory_device_pre_plug()

Let's move memory_device_check_addable() and basic checks out of
memory_device_get_free_addr() directly into memory_device_pre_plug().

Separating basic checks from address assignment is cleaner and
prepares for further changes.

As all memory device users now use memory_devices_init(), and that
function enforces that the size is 0, we can drop the check for an empty
region.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20230623124553.400585-10-david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>