NFC: move nfc.h from include/net to include/net/nfc

The file nfc.h was moved from include/net to include/net/nfc,
since new NFC header files will be added to include/net/nfc.

Signed-off-by: Ilan Elias <ilane@ti.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>