Update circular mask after display is ready.

This fixes the situation where the circular mask is not applied because
the configuration is not reporting round screen. Configuration is
computed based on the display, so we can only depend on it having the
correct information after the display became ready.

Bug: 23689649
Bug: 23325855
Change-Id: I1e1fa307836f4053cfc4978da0239cb42c5af2c3