package/libdrm: fix autoreconf

package/libdrm: fix autoreconf

To properly autoreconf, the xorg macros, from host-xutil_util-macros,
are needed.

Fixes:
    http://autobuild.buildroot.org/results/2e8/2e887c25b22bd36eab36ff361645306c8ddb79aa/
    http://autobuild.buildroot.org/results/7c0/7c0050d63a1d34eecb6d16e2654369cea561707a/
    http://autobuild.buildroot.org/results/2ef/2ef3d6d74c56632c012b85e05af6eaf0259b72c9/
    [...]

(Thanks Romain for confirming the fix on IRC! ;-) )

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Bernd Kuhls <bernd.kuhls@t-online.de>
Cc: Romain Naour <romain.naour@openwide.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>