CEC: Make port info unmodifiable

Puts HDMI port information behind unmodifiable type. This helps API make use
of port-related information without having to switch to service thread.
See getActiveSource().

Added the unmodifiable version of SparseArray/SparseIntArray.

Change-Id: Idcf05d1d6e19b47c91a7e89a920abccc607a3eb5