ARM: dts: N9/N950: add bluetooth

The Nokia N950 and N9 have a wl1271 (with nokia bootloader) bluetooth
module connected to second UART.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
Queued-by: Tony Lindgren <tony@atomide.com>

Changes since PATCHv1:
 - update compatible string