HDMICEC: Deprecate HdmiTvClient#getDeviceList

Move the implementation of the getDeviceList method from HdmiTvClient and HdmiSwitchClient to the HdmiClient abstract class in order to avoid duplicate code and to make it visible for HdmiPlaybackClient.

Add unit test for HdmiCecNetwork#getSafeCecDevicesLocked method which is
called by HdmiControlService#getDeviceList.

Bug: 196043550
Test: make && atest HdmiCecNetworkTest
Change-Id: If4727d582348022a0317d9fce6459d56a7affa5a