ARM: dts: N900: Add bluetooth

Add bcm2048 node and its system clock to the N900 device tree file.
Apart from that a reference to the new clock has been added to
wl1251 (which uses it, too).

Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>