Add xenlight to the un- and reinstall Makefile targets

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
xenlight: ifdef-away only the libxl functions that are not yet upstream

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
Merge pull request #20 from robhoes/master

xenlight: ifdef-away only the libxl functions that are not yet upstream