libxml-parser-perl: add LICENSE_FILES

There is copyright information in the top level README file. Use this
file as the license file which will be included by the `legal-info`
build rule.

Signed-off-by: Ben Leinweber <bleinweber@spaceflight.com>
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
(cherry picked from commit 730da52edc45f2b72fc1d522ff184276d20c8b0d)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libxml-parser-perl/libxml-parser-perl.mk

@@ -9,6 +9,7 @@ LIBXML_PARSER_PERL_SOURCE = XML-Parser-$(LIBXML_PARSER_PERL_VERSION).tar.gz
 LIBXML_PARSER_PERL_SITE = $(BR2_CPAN_MIRROR)/authors/id/T/TO/TODDR
 HOST_LIBXML_PARSER_PERL_DEPENDENCIES = host-expat
 LIBXML_PARSER_PERL_LICENSE = Artistic or GPL-1.0+
+LIBXML_PARSER_PERL_LICENSE_FILES = README
 LIBXML_PARSER_PERL_RUN_PERL = `which perl`
 
 define HOST_LIBXML_PARSER_PERL_CONFIGURE_CMDS