driver core: Split device_platform_notify()

Split device_platform_notify_remove) out of device_platform_notify()
and call the latter on device addition and the former on device
removal.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>