arm: orion5x: fix orion5x.dtsi gpio parameters

orion5x.dtsi is missing the gpio alias as well as including a typo
('ngpio' instead of 'ngpios') that prevented the orion-gpio driver
from loading.  Also missing were the interrupt-controller properties.
This patches resolves those glitches.

Signed-off-by: Alexander Clouter <alex@digriz.org.uk>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>