drm/gpusvm: Fix kernel-doc

drm/gpusvm: Fix kernel-doc

Due to wrong `.. kernel-doc` directive in Documentation/gpu/rfc/gpusvm.rst
the documentation was actually not parsing anything from
drivers/gpu/drm/drm_gpusvm.c. This fixes the kernel-doc include and all
warnings/errors created when doing so.

Cc: Simona Vetter <simona.vetter@ffwll.ch>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: dri-devel@lists.freedesktop.org
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/intel-xe/20250307195239.57abcd2d@canb.auug.org.au/
Fixes: 99624bdff867 ("drm/gpusvm: Add support for GPU Shared Virtual Memory")
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250307-fix-svm-kerneldoc-v2-1-03c74b199620@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>