Rather than waiting for each evict / restore of pinned BOs to complete
just wait on migrate exec queue to be idle once during suspend / resume.

Cc: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240305173503.285223-1-matthew.brost@intel.com