drm/xe/pf: Allow to control scheduling priority using debugfs

Add 'sched_priority' attribute that will represents the scheduling
prority of the VF or PF. Values {0,1,2} correspond to priorities
{LOW,NORMAL,HIGH} respectively.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Lukasz Laguna <lukasz.laguna@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241106151301.2079-5-michal.wajdeczko@intel.com