MediaCas: Reinit the CAS service if killed

When the MediaCasService is killed or dies, allow for it to be
re-initialized with the new instance of the service. The service is
restarted by the system, this code just re-initializes a pointer to this
new service.

Test: atest android.media.misc.cts.MediaCasTest
Bug: 327332440
Change-Id: I9d98c4e200adc4ee987dc8d1e472dfe5ac8f8da2