Input: i8042 - export i8042_command()

Export the i8042_command() function which manages the mutual
exclusion with the help of the i8042_lock spinlock. This allows
to access i8042 safely from other parts of the kernel.

Signed-off-by: Márton Németh <nm127@freemail.hu>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>