Use char instead of int in Tuner AIDL interface for all the 16-bit data defined in TunerHAL

char is char16_t in cpp backend when defined in AIDL interface.
See: https://source.android.com/devices/architecture/aidl/aidl-backends#types

Test: make
Bug: 185627837
Change-Id: Iecb6ae293e0ad46e80b29c558816705be1577d3f