module: make module_memory_{alloc,free} more self-contained

Move the logic related to the memory allocation and freeing into
module_memory_alloc() and module_memory_free().

Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>