Fix no output on second physical display

The RefreshRateConfigs only store the configs of default display
when init. But setAllowedDisplayConfigs would get NPE while getting
these configs from secondary display.
We need to cache the configs of external physical display when hotplug.

Bug: 127868178
Test: build and flash mojave device.
Change-Id: Ie1b598e8f77b28a444097deb0e05dda10d197db5
1 file changed