mali_kbase: APC: avoid unnecessary apc request

If a second apc request is coming while the first one is still powering
on the GPU, then the 2nd one should only update the apc.end_ts instead.
This change adds a apc.pending to help avoid the duplicate work.

If relative wake duration is not positive after GPU has been powered on,
call kbase_pm_context_idle directly after to cancel out instead of
queuing apc.power_off_work again.

Bug: 170337464
Test: systrace and latency sensitive workload
Signed-off-by: Yiwei Zhang <zzyiwei@google.com>
Change-Id: I24c5745770a0be49e872e4875f05f24afc7ec87e