bcma: use chipcommon node from DT for SoC GPIO chip

This will allow us to define GPIO-attached devices (LEDs, buttons) in
the the device tree.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>