drm/xe/guc: Introduce enum with offsets for context register H2Gs

Some GuC messages are constructed with incrementing dword counter
rather than referencing specific DWORDs, as described in GuC interface
specification.

This change introduces the definitions of DWORD numbers for parameters
which will need to be referenced in a CTB parser to be added in a
following patch. To ensure correctness of these DWORDs, verification
in form of asserts was added to the message construction code.

v2: Renamed enum members, added ones for single context registration,
  modified asserts to check values rather than indexes.
v3: Reordered assert args to take less lines
v4: Added lengths
v5: Renamed MULTI_LRC_MSG_LEN to MULTI_LRC_MSG_MIN_LEN

Suggested-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://lore.kernel.org/r/20250512114018.361843-4-tomasz.lis@intel.com