drm/xe: Move Media GuC register definition to regs/

This GuC register can be moved together with the rest of the
GuC register definitions and be named in a similar way.

v2: fix placement

Bspec: 63363
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com> #v1
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>