xen: merge temporary vcpu pinning scenarios

xen: merge temporary vcpu pinning scenarios

Today there are two scenarios which are pinning vcpus temporarily to
a single physical cpu:

- wait_event() handling
- SCHEDOP_pin_override handling

Each of those cases are handled independently today using their own
temporary cpumask to save the old affinity settings.

The two cases can be combined as the first case will only pin a vcpu to
the physical cpu it is already running on, while SCHEDOP_pin_override is
allowed to fail.

So merge the two temporary pinning scenarios by only using one cpumask
and a per-vcpu bitmask for specifying which of the scenarios is
currently active (they are both allowed to be active for the same vcpu).

Note that we don't need to call domain_update_node_affinity() as we
are only pinning for a brief period of time.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>