ARM: dts: add minimal DT support for Nokia N950 & N9 phones

Add minimal DT support for Nokia N950 & N9 phones. The same functionality
that is provided by the current board file should work: serial console,
USB, OneNAND and MMC.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Tony Lindgren <tony@atomide.com>