input: i8042: Use remove() instead of exported functions

input: i8042: Use remove() instead of exported functions

We should not have exported functions in a driver. The i8042_disable()
function is used to disable the keyboard. Provide a remove() method
instead, which is the standard way of disabling a device.

We could potentially add a method to flush input but that does not seem
necessary.

Signed-off-by: Simon Glass <sjg@chromium.org>