mali_kbase: probe: Add dependency on MGM

Since mali_kbase.ko requires the memory group manager
to have been loaded to avoid needing to defer its
probe, we add a hint here to indicate that the system
should load memory_group_manager.ko first.

Signed-off-by: Sidath Senanayake <sidaths@google.com>
Change-Id: I0f03dddb25237e83e5f0dae65517e139afa3c2c2