Not Implemented response for unsupported AVRCP commands.

Ensure DUT responds as not implemented for AVRCP
pass-through commands which are not supported by DUT.
This gives right impression to peer device on the correct
set of pass-thorugh commands supported by DUT.

Bug: 21896912
Change-Id: Ie10e74e2a399bb420f55c55005600c945b53bfc2