ARM: dts: armv7-m: add unit name to interrupt-controller

Add unit name to nvic to remove the following warning:
 Warning (unit_address_vs_reg): Node /nv-interrupt-controller has a reg or ranges property, but no unit name

Also correct the node name to 'interrupt-controller'
while changing the line.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Stefan Agner <stefan@agner.ch>