drm/xe: Add helpers to loop over geometry and compute DSS

Some DSS can only be available for geometry while others can only be
available for compute.
So here adding helpers to loop only available DSS for given usage.

User of this helper will come in the next patch.

v2:
- drop has_dss()

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Zhanjun Dong <zhanjun.dong@intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240424140319.61651-2-jose.souza@intel.com