extras/keymap: Rename KEY_COFFEE to KEY_SCREENLOCK

extras/keymap: Rename KEY_COFFEE to KEY_SCREENLOCK

Unfortunately KEY_COFFEE is the canonical name in linux/input.h, and the more
sensible KEY_SCREENLOCK is an alias. Manually override this particular case,
since it's better to have "screenlock" in keymaps.

However, we still keep the automatic filtering for the general case, to avoid
introducing this problem again when input.h changes.