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>

SVN-Revision: 42180