FogBugz #166591: Rocketboards poky builds using wrong toolchain

This fix is to change the toolchain used to build poky if it is pulled
from RBO

Signed-off-by: Tien Hock Loh <thloh@altera.com>
Fogbugz #166591 : Rocketboard build toolchain fix - change relative path to full path

Signed-off-by: Lee Booi Lim <lblim@altera.com>