ARM: dts: mmp2: Add SSP controllers

Despite Marvel keeps their base addresses secret there's a good chance
they're actually correct.

SSP1 and SSP3 bases were taken from OLPC 1.75: OpenFirmware and kernel
respectively. SSP2 and SSP4 addresses are from James Cameron who actually
has a copy of the data sheet.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Olof Johansson <olof@lixom.net>