package/x11r7/xutil_makedepend: add missing dependency on host-pkgconf

package/x11r7/xutil_makedepend: add missing dependency on host-pkgconf

The configure script of xutil_makedepend uses PKG_CHECK_MODULES(), so
it should depend on host-pkgconf. Otherwise, a "make
host-xutil_makedepend" fails with:

"""
checking for X... configure: error: in `/home/thomas/projets/buildroot/output/build/host-xutil_makedepend-1.0.5':
configure: error: The pkg-config script could not be found or is too old.  Make sure it
is in your PATH or set the PKG_CONFIG environment variable to the full
path to pkg-config.

Alternatively, you may set the environment variables X_CFLAGS
and X_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.

To get pkg-config, see <http://pkg-config.freedesktop.org/>.
"""

This was detected using per-package host/target directories, but can
be reproduced without it.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>