libxslt: add --without-python to host package

Signed-off-by: Alexander Dahl <post@lespocky.de>
Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>
libxml2: update to 2.9.2

Also integrated two changes from upstream fixing two minor issues.
Build successfully tested against all ptxdist packages requiring
libxml2, no runtime tests.

Signed-off-by: Alexander Dahl <post@lespocky.de>
Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>