drm/i915/guc: Rename guc_ggtt_offset to intel_guc_ggtt_offset

GuC related exported functions should start with "intel_guc_" prefix and
pass intel_guc as the first parameter since its GuC related. Current
guc_ggtt_offset() failed to follow this code convention and this is a
problem for future patches that needs to access intel_guc data to verify
the GGTT offset against the GuC WOPCM top.

This patch renames the guc_ggtt_offset to intel_guc_ggtt_offset and updates
the related code to pass intel_guc pointer to this function call, so that
we can have a unified coding style for GuC code and also enable the future
patches to get GuC related data from intel_guc to do the offset
verification. Meanwhile, this patch also moves the GUC_GGTT_TOP from
intel_guc_regs.h to intel_guc.h since it is not GuC register related
definition.

v8:
 - Fixed coding style issues and moved GUC_GGTT_TOP to intel_guc.h (Sagar)
 - Updated commit message to explain to reason and motivation to add
   intel_guc as the first parameter of intel_guc_ggtt_offset (Chris)

v9:
 - Fixed code alignment issue due to line break (Chris)

v10:
 - Removed unnecessary comments, redundant code and avoided reuse variable
   to avoid potential issues (Joonas)

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

Signed-off-by: Jackie Li <yaodong.li@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Sagar Arun Kamble <sagar.a.kamble@intel.com> (v8)
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/1520987574-19351-1-git-send-email-yaodong.li@intel.com