Pass BTN_GEAR_DOWN and BTN_GEAR_UP to apps

The Steam controller has 2 large 'paddle' buttons on the back. When used
in USB mode with hid-steam, this sends BTN_GEAR_DOWN and BTN_GEAR_UP to
the user space.

But today, these events never reach the apps, even if they have proper
mappings. This is because these buttons are not considered to be
"keyboard or gamepad". Adjust the checks to include these 2 buttons in
KeyboardInputMapper.

Test: connect Steam controller over USB and check that the paddle
buttons produce events visible in the "gamepad tester" app
Test: atest inputflinger_tests
Bug: 147434575

Change-Id: I43f221c546ccc1277d578a185465bd5eadac9e8e