drm/i915: Clean up kerneldoc for intel_lrc.c

Fairly minimal, there's still lots of functions without any docs, and
which aren't static. But probably we want to first clean this up some more.

- Drop the bogus const. Marking argument pointers themselves (instead of
  what they point at) as const provides roughly 0 value. And it's confusing,
  since the data the pointer points at _is_ being changed.

- Remove kerneldoc for static functions. Keep comments where they seem valuable.

- Indent and whitespace fixes.

- Blockquote the bit field definitions of the descriptor for correct layouting.

Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1468612088-9721-9-git-send-email-daniel.vetter@ffwll.ch