xentrace: formats: update format of scheduling events

xentrace: formats: update format of scheduling events

to include the vcpu IDs, in a way that matches
how the "dom:vcpu" couple is displayed in other
events (runstate changes).

Also add the trace for TRC_SCHED_SHUTDOWN_CODE which
was missing and was done via SCHEDOP_shutdown_code hypercall.
(TRC_SCHED_SHUTDOWN trace was present).

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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Cc: George Dunlap <george.dunlap@eu.citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: Olaf Hering <olaf@aepfle.de>
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Changes from v1:
 * enhanced changelog, as suggested during review.