drm: panel: s6e3hc3: implement minimum idle refresh rate

Respect the value set in min_vrefresh sysfs node to allow the target
refresh rate when display becomes idle.
This includes different auto mode step settings for target idle refresh
rates (10hz, 30hz or 60hz).

Bug: 203002919
Signed-off-by: Adrian Salido <salidoa@google.com>
Change-Id: I46264373cbad5c703523b1b947fcbe30ecf88257