The BCTs are build objects and as such are located in the objtree instead of
the srctree. Fix out-of-tree build by defining a variable which refers to the
board directories in the objtree and use it for Tegra.
Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>