freetype: fix staging headers

freetype: fix staging headers

freetype 2.5.1 moved headers from /usr/include/freetype2/freetype to
/usr/include/freetype2.
Some packages use a non-recommended header inclusion of <freetype/x.h>
instead of using the recommended ft2build.h method, so until it's fixed
across the board upstream for packages that break do a symlink.

See:
http://git.savannah.gnu.org/cgit/freetype/freetype2.git/commit/?id=fae382076409db198dfbff36ac4cbb97b05b30a1

Fixes:
http://autobuild.buildroot.net/results/64c/64cc8467eeb44f741aeb42bf1a0c77edbfbd285f/
http://autobuild.buildroot.net/results/708/708fa7423c83e22a51854f1abca0f3358506a318/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>