mali_kbase: Update platform interface with additional callbacks

Adds additional (optional) callbacks for kbase_context and
kbase_jd_atom events. Integrators that implement handlers for
these callbacks receive events for context initialization and
termination, as well as for atom submission and completion.

Bug: 171975331
Signed-off-by: Sidath Senanayake <sidaths@google.com>
Change-Id: I1de49460b71a6ec36e0b9ca88dd2715b323c13f3