Revert "Don't install /var/db/dhcpcd in the Makefile"

This was when the privsep code had the database directory in the
chroot, which it not longer is.

This reverts commit 5f275b7.

src/Makefile

@@ -82,6 +82,7 @@ _embeddedinstall: ${DHCPCD_DEF}
 _proginstall: ${PROG}
 	${INSTALL} -d ${DESTDIR}${SBINDIR}
 	${INSTALL} -m ${BINMODE} ${PROG} ${DESTDIR}${SBINDIR}
+	${INSTALL} -d ${DESTDIR}${DBDIR}
 
 proginstall: _proginstall ${EMBEDDEDINSTALL}
 	for x in ${SUBDIRS}; do cd $$x; ${MAKE} $@ || exit $$?; cd ..; done