input: Wake on natigation button without keyguard

Refactored the code a bit to handle WM_ACTION_POKE_USER_ACTIVITY
when using the navigation button wake without the KeyGuard active.

Tried to avoid code duplication, but we may want to move the
navigation button handling to a separate function in the policy to
avoid the BTN_MOUSE keyCode hack at some point.

Change-Id: I5545d99aaf4ea1ffe044c9f124d8397f25c31f3a