Add Setting for HDMI CEC 2.0

Introduce Settings.Global.hdmi_cec_version. Stores an integer value
based on the CEC version constants defined in the HDMI-CEC
specification.

Defaults to v1.4b.

Bug: 166227067
Test: atest HdmiControlServiceTest
Change-Id: If3d85991230c00af4482076d90bf9a730ab385ae