Add keylayout mapping for Luna controller (Bluetooth)

Add a keylayout mapping to support gamepad buttons and axes on the
Amazon Luna controller.

Buttons and axes are mapped according to
https://www.kernel.org/doc/Documentation/input/gamepad.txt except for
the Alexa Push-To-Talk button which is mapped to MEDIA_RECORD.

Bug: 183990549
Test: used the "Gamepad Tester" app and https://gamepad-tester.com in
Chrome to verify all mappings work.

Change-Id: I1921e501eea0ce398b79a32809efa63456074ed5