ARM: dts: vf610-zii-dev-rev-b: fix interrupt for GPIO expander

The interrupt specification for the GPIO expander is wrong - the
expander is wired to PTB28, which is GPIO98.  GPIO98 is on gpio chip
3, not 2.

In addition, the device is missing a required property.  Interrupt
controllers must have the "interrupt-controller" property specified.
Add this.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>