mali_kbase: pm: Enhance power policy interface

Extends the power management policy interface to allow
for more complex power policies to be implemented by:

(1) Adding a 'handle_event' function which can accept
incoming power events from the GPU power state machine.
Also updates the GPU power state machine implemented in
`kbase_pm_shaders_update_state` to emit such events.

(2) Allow for the power policy to modify the number of
ticks that the shader tick timer runs for. This is
implemented by adding a new field element that retains
the compile time & sysfs updated value for the number
of ticks, leaving the existing `configured_ticks`
element to be modified by the power policy. For simple
power policies, this results in no change.

(3) Add logic to automatically clear per-power policy
private data when switching between power policies.
This reduces the amount of cleanup that each power
policy needs to do on init/term.

These allow for more advanced power policies to be
implemented.

Bug: 183700775
Signed-off-by: Sidath Senanayake <sidaths@google.com>
Change-Id: I81766b7c97691fec2496f60d91b00476277b2fe7