arm: tegra2: fix out-of-tree build

arm: tegra2: fix out-of-tree build

The out-of-tree build fails because the Makefiles in question depend on
source files of another directory but do not explicitly mkdir that
directory.

As a matter of fact, other Makefiles under board/*/ directory that refer
to source files under another directory explicitly call mkdir.

This patch adds explicit mkdir's to the Makefiles in question, and
verifies that out-of-tree build is working.

Signed-off-by: Che-Liang Chiou <clchiou@chromium.org>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>