mali_kbase: platform: power: Explicitly track GPU power state

Store the view of GPU power state within the GPU platform integration
itself rather than relying on querying PMU registers.

Test: run cts-dev --include-filter "CtsDeqpTestCases dEQP-VK.protected_memory.*"
Test: Repro steps for race condition from b/196269975#comment71
Test: Ensure inter-frame power off working
Bug: 196269975
Bug: 196300136
Signed-off-by: Sidath Senanayake <sidaths@google.com>
Change-Id: I86f9472b0a43139f28d78cd858608f054910b7ed