drm/i915/gt: allow setting generic data pointer

drm/i915/gt: allow setting generic data pointer

When registering debugfs files the intel gt debugfs library
forces a 'struct *gt' private data on the caller.

To be open to different usages make the new
"intel_gt_debugfs_register_files()"[*] function more generic by
converting the 'struct *gt' pointer to a 'void *' type.

I take the chance to rename the functions by using "intel_gt_" as
prefix instead of "debugfs_", so that "debugfs_gt_register_files()"
becomes "intel_gt_debugfs_register_files()".

Signed-off-by: Andi Shyti <andi.shyti@intel.com>
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/20200326181121.16869-2-daniele.ceraolospurio@intel.com