drm/i915/guc: Break out the GuC log extras into their own "runtime" struct

When initializing the GuC log struct, there is an object we need to
allocate always, since the GuC needs its address at fw load time.
The rest is only needed during runtime, in the sense that we only
create if we actually enable GuC logging. Make that distinction
explicit by subdividing further the intel_guc_log struct.

v2: Call the new struct "runtime", instead of "extras" (Joonas)

v3: Check indent (Joonas)

Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>