ar71xx: add a new driver for the ar7240 switch using swconfig. hooks directly...

ar71xx: add a new driver for the ar7240 switch using swconfig. hooks directly into the ethernet driver, as MAC resets also require switch reinitializations and the switch is part of the cpu core anyway switch only tl-wr741nd (and other devices using this board file, such as tl-wr841nd) over to using this by default, as other devices are still untested fixes #7563

SVN-Revision: 22675