HID: core: remove #ifdef CONFIG_PM from hid_driver

Allow HID drivers to pass ->suspend, ->resume and ->reset_resume via
pm_ptr().
Through the usage of pm_ptr() the CONFIG_PM-dependent code will always be
compiled, protecting against bitrot.
The linker will then garbage-collect the unused function avoiding any overhead.

The only overhead in the final kernel image and at runtime are a few
extra bytes in 'struct hid_driver'.

The same approach is chosen by 'struct usb_driver' and other subsystems.

Signed-off-by: Thomas Weißschuh <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Benjamin Tissoires <[e-mail]>

include/linux/hid.h

···
 	void (*feature_mapping)(struct hid_device *hdev,
 			struct hid_field *field,
 			struct hid_usage *usage);
-#ifdef CONFIG_PM
+
 	int (*suspend)(struct hid_device *hdev, pm_message_t message);
 	int (*resume)(struct hid_device *hdev);
 	int (*reset_resume)(struct hid_device *hdev);
-#endif
+
 /* private: */
 	struct device_driver driver;
 };