lantiq: improve ARV7519RW22 support

- use full board name
- rename uboot-env partition
- add dsl_fw partition
- remove unneeded pinmux groups
- move gigabit ethernet to LAN
- load mac address from mtd

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42180 3c298f89-4303-0410-b956-a3cf2f4a3e73