libsoc: add host-pkgconf dependency

Without pkg-config PKG_CHECK_MODULES won't be expanded
and ./configure script produces following error message:

./configure: line 12237: syntax error near unexpected token `PYTHON,'
./configure: line 12237: `	PKG_CHECK_MODULES(PYTHON, python-"$PYTHON_VERSION")'

Fixes:

http://autobuild.buildroot.net/results/86e/86e04bd2b10527130306451e56a7693ed4b4befd

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/libsoc/libsoc.mk

@@ -10,6 +10,7 @@ LIBSOC_LICENSE = LGPL-2.1
 LIBSOC_LICENSE_FILES = LICENCE
 LIBSOC_AUTORECONF = YES
 LIBSOC_INSTALL_STAGING = YES
+LIBSOC_DEPENDENCIES = host-pkgconf
 
 # Install Python 2 bindings
 ifeq ($(BR2_PACKAGE_PYTHON),y)