drm/xe: Move engine base offsets to engine register header

These offsets are primarily used as parameters for the engine register
definitions, so it makes more sense to define them in the engine header
rather than the general register header.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20231214184659.2249559-14-matthew.d.roper@intel.com


Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>