SF: Fix unit tests re-registering a display

As written, these tests register a PhysicalDisplayId with a
RefreshRateSelector while setting up their TestableSchedulers, and then
later register the same PhysicalDisplayId with a different
RefreshRateSelector. While the tests pass as is, along with
Icdb80253436b4d0034fc20fcae8583efb7c30292, this causes the tests to
fail.

Update the failing tests to skip registering the PhysicalDisplayId
because it's already been registered and to use the same
RefreshRateSelector in the FakeDisplayDeviceInjector.

Bug: 241285191
Test: libsurfaceflinger_unittest
Change-Id: Ib147ce14995cc5544812aab2c788ad046124d292