Since the NFC subsystem gained RFKILL support, it needs to be able
to build properly with whatever option for RFKILL has been selected.

on i386:

net/built-in.o: In function `nfc_unregister_device':
(.text+0x6a36d): undefined reference to `rfkill_unregister'
net/built-in.o: In function `nfc_unregister_device':
(.text+0x6a378): undefined reference to `rfkill_destroy'
net/built-in.o: In function `nfc_register_device':
(.text+0x6a493): undefined reference to `rfkill_alloc'
net/built-in.o: In function `nfc_register_device':
(.text+0x6a4a4): undefined reference to `rfkill_register'
net/built-in.o: In function `nfc_register_device':
(.text+0x6a4b3): undefined reference to `rfkill_destroy'
net/built-in.o: In function `nfc_dev_up':
(.text+0x6a8e8): undefined reference to `rfkill_blocked'

when CONFIG_RFKILL=m but NFC is builtin.
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>