libxml-parser-perl/intltool: mark as host only packages

libxml-parser-perl and intltool were originally added to be built on
the host, and we don't support building them on the target. So, let's
mark them as such in the configuration, so that a random package
configuration does not pick them up. We might later add target support
for them.

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