drm/i915/uc: Move uC debugfs to its own folder under GT

uC is a component of the GT, so it makes sense for the uC debugfs files
to be in the GT folder. A subfolder has been used to keep the same
structure we have for the code.

v2: use intel_* prefix (Jani), rebase on new gt_debugfs_register_files,
fix permissions for writable debugfs files.

v3: Rename files (Michal), remove blank line (Jani), fix sparse warns.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Andi Shyti <andi.shyti@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Tony Ye <tony.ye@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: Andi Shyti <andi.shyti@intel.com> #v2
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200326181121.16869-6-daniele.ceraolospurio@intel.com