drm/i915: Fix GuC documentation links

drm/i915: Fix GuC documentation links

We moved GuC related files to new location but we missed to update
.rst file with links.

References: commit 91a9d71b0122 ("drm/i915/uc: move GuC and HuC files under gt/uc/")
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190725141308.24660-1-michal.wajdeczko@intel.com