Otherwise we may run into following:

drivers/platform/built-in.o: In function `i8042_lock_chip':
/home/test/ws2/projects/linux-2.6/include/linux/i8042.h:50: multiple definition of `i8042_lock_chip'
drivers/input/serio/built-in.o:/home/test/ws2/projects/linux-2.6/include/linux/i8042.h:50: first defined here
...
make[1]: *** [drivers/built-in.o] Error 1
make: *** [drivers] Error 2

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>