drm/xe: Invert runnable_state / pending enable check and assert

Rather than checking for pending enable and asserting runnable_state ==
1 in sched done handler, invert these. This is more robust code taking
action based on the G2H message and asserting KMD tracking state is
correct.

Suggested-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240614061343.2931649-1-matthew.brost@intel.com