brcm47xx: board detection, GPIO for Linksys E1000 V2.1

This patch adds board detection for the Linksys E1000 V2.1 router, as well
as GPIO support for same.

This fixes bug #14135. Currently, wired networking isn't working on the
router, and I haven't tried the wireless, but with this patch, OpenWRT
successfully boots, and all the LEDs and buttons work properly.

Signed-off-by: Zachary Catlin <zcatlin@indiana.edu>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

SVN-Revision: 37977