HSI: nokia-modem: add n950 and n9 support

The Nokia N950 and Nokia N9 also have a SSI connected
modem, which use the same protocols as the Nokia N900,
but with increased link speed (96000 kbps instead of
55000 kbps) and with less GPIOs.

Since it's unclear, if the N950 and the N9 use exactly
the same modem, each of them gets their own compatible
string.

Acked-by: Rob Herring <robh@kernel.org>
Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Sebastian Reichel <sre@kernel.org>