drm/i915/gt: Remove stale kerneldoc for internal MOCS functions

The kerneldoc were stale, generating mismatching parameters warning, but
furthermore they were for internal routines, not part of the MOCS
interface so the instructions were superfluous.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190803102221.21344-1-chris@chris-wilson.co.uk