python-markupsafe: allow build as host package

python-markupsafe is a dependency for python-jinja2, which can be used
during build time as a host tool to generate code based on templates.
This package is being added host package support mostly to allow
host-python-jinja2 to build.
This has been tested to build and work correctly as a host tool as well.

Signed-off-by: Erico Nunes <erico.nunes@datacom.ind.br>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>