asdk-libdrm

man: convert manpages to XML instead of plain troff

If we want to use the manpages in external documentation other than normal
manpages, we should rather use XML. Furthermore, almost no-one knows troff
today, anyway, and XML allows others to easily add more pages without
having to learn troff.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>