Input: i8042 - force synchronous probing of PNP drivers

We rely on the result of scanning PNP bus for keyboard and mouse devices to
decide whether we should continue initialization of i8042 driver or not, so
the probes can not be asynchronous.

Also, it is not a good idea to unbind either of the PNP devices while i8042
is running, so let's disable bind/unbind for the PNP drivers through sysfs
and rely on i8042 cleaning after itself properly. User can still unbind and
rebind entire i8042 and that will take care of PNP drivers as well.

Reviewed-by: Luis R. Rodriguez <mgrof@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>