xen: Introduce vcpu_sleep_nosync_locked()

xen: Introduce vcpu_sleep_nosync_locked()

There are a lot of places which release a lock before calling
vcpu_sleep_nosync(), which then just grabs the lock again.  This is
not only a waste of time, but leads to more code duplication (since
you have to copy-and-paste recipes rather than calling a unified
function), which in turn leads to an increased chance of bugs.

Introduce vcpu_sleep_nosync_locked(), which can be called if you
already hold the schedule lock.

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>