drm/xe: Translate C-state "reset value" into RC6

drm/xe: Translate C-state "reset value" into RC6

There are higher level sleep states that will cause RC6 state readout to
come back with an "in-reset" value. That is the case with NVL-P. As
those states are only possible if the GT is already in C6, let's just
translate the "reset value" into C6 when doing the readout.

Bspec: 67651
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patch.msgid.link/20260309-extra-nvl-p-enabling-patches-v5-7-be9c902ee34e@intel.com
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>