SF: update kernel idle timer when active display changes

The refresh rate policy for a display might change when it is not
the active display, and when this display becomes active, we need
to update the kernel timer to reflect the updated policy.

Bug: 188838426
Test: check graphics.display.kernel_idle_timer.enabled is updated
      according to the most updated policy when switching active
      display.
Change-Id: I94ee9a019e4f38bf1bd28202144dbc30af2f9261