panel: common: add option to delay idle based mode sets

This adds a way to throttle how fast we can go into idle after last
mode set was called based on threshold set via "idle_delay_ms" sysfs
node. This helps prevent refresh rate updates from happening too often.

Bug: 203002561
Signed-off-by: Adrian Salido <salidoa@google.com>
Change-Id: I25e31dee3ee51a058fae9ad2f9e5a736cc6fae82