drm/i915/guc: Refactoring preparation of the GUC_CTL_LOG_PARAMS parameter

At the moment, the preparation of GUC_CTL_LOG_PARAMS is disordered.
Additionally, in struct intel_guc_log we have an unnecessary field
'flags' which we use only to assign value to GuC parameter.
Lets move all GUC_CTL_LOG_PARAMS related operations to one place,
and lets remove field 'flags' from struct intel_guc_log.

Signed-off-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180604141947.8299-4-piotr.piorkowski@intel.com