MIPS: JZ4740: qi_lb60: Add gpio-charger device

Register the gpio-charger device which reports whether device is currently
charging or not.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/2059/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>