HID: rmi: fallback to generic/multitouch if hid-rmi is not built

Commit 279967a6 ("HID: rmi: Handle all Synaptics touchpads using hid-rmi")
unconditionally switches over handling of all Synaptics touchpads to hid-rmi
(to make use of extended features of the HW); in case CONFIG_HID_RMI is
disabled though this renders the touchpad unusable, as the

	HID_DEVICE(HID_BUS_ANY, HID_GROUP_RMI, HID_ANY_ID, HID_ANY_ID)

match doesn't exist and generic/multitouch doesn't bind to it either (due
to hid group mismatch).

Fix this by switching over to hid-rmi only if it has been actually built.

Fixes: 279967a6 ("HID: rmi: Handle all Synaptics touchpads using hid-rmi")
Reported-by: NLinus Torvalds <torvalds@linux-foundation.org>
Acked-by: NBenjamin Tissoires <benjamin.tissoires@redhat.com>
Tested-by: NAndrew Duggan <aduggan@synaptics.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/hid-core.c

@@ -827,7 +827,8 @@ static int hid_scan_report(struct hid_device *hid)
 				 * hid-rmi should take care of them,
 				 * not hid-generic
 				 */
-				hid->group = HID_GROUP_RMI;
+				if (IS_ENABLED(CONFIG_HID_RMI))
+					hid->group = HID_GROUP_RMI;
 		break;
 	}