panel: nt37290: throttle auto mode when idle_delay is set

Auto mode gets re-triggered every time there is a new commit. In
order to prevent refresh rate updates from happening too often (
based on "idle_delay_ms" sysfs node), delay auto mode re-triggering
when the delay is set.

This leads to switching to manual mode refresh rate update until
the delay has elapsed, then it switches back to auto mode while
updating continuously. The hibernation (via set_self_refresh call)
will make it switch back to auto mode as well.

Bug: 209360090
Test: set idle_delay_ms and check the logs
Change-Id: I31f16888f0f9fb9a270ebbf2d27b29486306c526
Signed-off-by: Chris Lu <luchris@google.com>