Support of xl sched-sedf

Support of xl sched-sedf

Supports the xl subcommand sched-sedf.
The man page is only a minimal version (copy from xm man page without
examples). BTW: the xm man page seems not to be in sync with xm sched-sedf -h
regarding the time units. I used milliseconds in the xl implementation.
Only minimal semantical checks of parameters.

Signed-off-by: juergen.gross@ts.fujitsu.com
Acked-by: Ian Jackson <ian.jackson.citrix.com>
Committed-by: Ian Jackson <ian.jackson.citrix.com>