ar71xx: add preliminary support for Mikrotik RB2011L

This patch adds preliminary support for the Mikrotik RB2011L.
The NAND flash is not yet supported, so only the initramfs
kernel can be used for now.

[juhosg: remove unnecessary PCI/USB related stuff, the board
does not use that, update commit message]

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>

SVN-Revision: 33344