[brcm63xx] remove references to the old switch driver

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@35503 3c298f89-4303-0410-b956-a3cf2f4a3e73
[brcm63xx] remove superfluous calls to /lib/brcm63xx.sh

The first preinit script 03_do_brcm63xx.sh does the right job of
exporting variables for the other subsequent preinit scripts to use
them.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@35504 3c298f89-4303-0410-b956-a3cf2f4a3e73
[brcm63xx] make default version 3.7.6

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@35505 3c298f89-4303-0410-b956-a3cf2f4a3e73
[brcm63xx] remove support for 3.6 kernel

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@35506 3c298f89-4303-0410-b956-a3cf2f4a3e73