ar71xx: rb2011: use the new RouterBOOT helpers

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39094 3c298f89-4303-0410-b956-a3cf2f4a3e73
ar71xx: rb2011: simplify setup code

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39095 3c298f89-4303-0410-b956-a3cf2f4a3e73