Add support for rpi zero

[Dreaded-Gnu]

Once rpi2b support is almost done, rpi zero support shall be added. Possible duplicate code in virtual memory handling and armv6 mmus support will be handled with issue #23

• Check and add for further necessary changes ( possibly task switch and more )

[Dreaded-Gnu]

With added support of raspi0_1, the following boards should also be added ( same technical specs ):

• raspi1a
• raspi1ap
• raspi1b
• raspi1bp