drm/i915: Add support to return CNL specific reserved WOPCM size

CNL has its specific reserved GuC WOPCM size for RC6 and other hardware
contexts.

This patch updates the code to return CNL specific reserved GuC WOPCM size
for RC6 and other hardware contexts so that the GuC WOPCM size can be
calculated correctly for CNL.

v9:
 - Created a new patch for these changes originally made in v8 4/6 patch of
   this series (Sagar/Michal)

v10:
 - Used if-else ladder to the returning of context sizes (Joonas)

v11:
 - Removed GUC_ prefix from context size macro (Michal)

v13:
  - Updated the ordering of s-o-b/cc/r-b tags (Sagar)

Bspec: 12690

Signed-off-by: Jackie Li <yaodong.li@intel.com>
Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> (v9)
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com> (v11)
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> (v12)
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1520987574-19351-3-git-send-email-yaodong.li@intel.com