driver-core: add test module for asynchronous probing
This test module tries to test asynchronous driver probing by having a
driver that sleeps for an extended period of time (5 secs) in its
probe() method. It measures the time needed to register this driver
(with device already registered) and a new device (with driver already
registered). The module will fail to load if the time spent in register
call is more than half the probing sleep time.
As a sanity check the driver will then try to synchronously register
driver and device and fail if registration takes less than half of the
probing sleep time.