ARM: mmp: add support for MMP3 SoC

Similar to MMP2, which this patch is based on. Known differencies from MMP2
are:

* Two PJ4B cores instead of one PJ4
* Tauros 3 L2 cache controller instead of Tauros 2
* A GIC interrupt controller optionally used instead of the MMP one
* A TWD local timer
* Different USB2 PHY
* A USB3 SS controller
* More interrupt muxes

Hard to tell what else is different, because documentation is not
available.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>