drm/i915/guc: Rename i915_guc_submission.c|h to intel_guc_submission.c|h

drm/i915/guc: Rename i915_guc_submission.c|h to intel_guc_submission.c|h

With all component structures and functions named appropriately, change
the names of GuC submission source files. There were bunch of style issues
in guc_submission.c that are highlighted now by checkpatch. Fix those.
Update name in Documentation/gpu. (Joonas)

v2: Rebase.

v3: Rebase.

Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Michal Winiarski <michal.winiarski@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1510839162-25197-6-git-send-email-sagar.a.kamble@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>