usb: typec: Send uevent for num_altmodes update

Generate a change uevent when the "number_of_alternate_modes" sysfs file
for partners and plugs is updated by a port driver.

Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Benson Leung <bleung@chromium.org>
Signed-off-by: Prashant Malani <pmalani@chromium.org>
Link: https://lore.kernel.org/r/20210107034904.4112029-1-pmalani@chromium.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>