We assumed that for all modern GENs the PTEs and register space are
split in the GTTMMADR BAR, but while it is true, we should rather use
fixed offset as it is defined in the specification.

Bspec: 4409, 4457, 4604, 11181, 9027, 13246, 13321, 44980
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: CQ Tang <cq.tang@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210926201005.1450-1-michal.wajdeczko@intel.com