ACPI / scan: Allow ACPI drivers to bind to PNP device objects

We generally don't allow ACPI drivers to bind to ACPI device objects
that companion "physical" device objects are created for to avoid
situations in which two different drivers may attempt to handle one
device at the same time.  Recent ACPI device enumeration rework
extended that approach to ACPI PNP devices by starting to use a scan
handler for enumerating them.  However, we previously allowed ACPI
drivers to bind to ACPI device objects with existing PNP device
companions and changing that led to functional regressions on some
systems.

For this reason, add a special check for PNP devices in
acpi_device_probe() so that ACPI drivers can bind to ACPI device
objects having existing PNP device companions as before.

Fixes: eec15edb (ACPI / PNP: use device ID list for PNPACPI device enumeration)
Link: https://bugzilla.kernel.org/show_bug.cgi?id=81511
Link: https://bugzilla.kernel.org/show_bug.cgi?id=81971Reported-by: Gabriele Mazzotta <gabriele.mzt@gmail.com>
Reported-by: Dirk Griesbach <spamthis@freenet.de>
Cc: 3.16+ <stable@vger.kernel.org> # 3.16+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/scan.c

@@ -975,7 +975,7 @@ static int acpi_device_probe(struct device *dev)
 	struct acpi_driver *acpi_drv = to_acpi_driver(dev->driver);
 	int ret;
 
-	if (acpi_dev->handler)
+	if (acpi_dev->handler && !acpi_is_pnp_device(acpi_dev))
 		return -EINVAL;
 
 	if (!acpi_drv->ops.add)