Add support for rpi 3b

[Dreaded-Gnu]

Once rpi2b support is almost done, rpi 3b support shall be added. Possible duplicate code in virtual memory handling will be cleaned up with issue #23

• Add 64 bit support

[Dreaded-Gnu]

With added support of raspi3b, the following boards should also be added ( same technical specs ):

• raspi2b_r2