drm/xe/guc: Update CSS header structures

Rework the CSS header structure according to recent updates to the GuC
API spec. Also include more field definitions.

v2: Also pass the new GuC specific structure to a GuC specific
function instead of the higher level, generic structure (review
feedback from Daniele).
Also correct naming of CSS_TIME_* fields.

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://lore.kernel.org/r/20250910210237.603576-2-John.C.Harrison@Intel.com