drm/xe: Move HW GGTT definitions to dedicated file

It's better to keep all hardware GGTT definitions separated from
the driver code. It also helps to avoid duplicated definitions.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240326131042.319-1-michal.wajdeczko@intel.com