drm/vmwgfx/vmwgfx_ttm_buffer: Supply some missing parameter descriptions

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:275: warning: Function parameter or member 'p_offset' not described in 'vmw_piter_start'
 drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:676: warning: Function parameter or member 'evict' not described in 'vmw_move_notify'

Cc: VMware Graphics <linux-graphics-maintainer@vmware.com>
Cc: Roland Scheidegger <sroland@vmware.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210115181313.3431493-12-lee.jones@linaro.org

drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c

@@ -265,6 +265,7 @@ static dma_addr_t __vmw_piter_sg_addr(struct vmw_piter *viter)
  *
  * @viter: Pointer to the iterator to initialize
  * @vsgt: Pointer to a struct vmw_sg_table to initialize from
+ * @p_offset: Pointer offset used to update current array position
  *
  * Note that we're following the convention of __sg_page_iter_start, so that
  * the iterator doesn't point to a valid page after initialization; it has
@@ -664,6 +665,7 @@ static int vmw_ttm_io_mem_reserve(struct ttm_bo_device *bdev, struct ttm_resourc
  * vmw_move_notify - TTM move_notify_callback
  *
  * @bo: The TTM buffer object about to move.
+ * @evict: Unused
  * @mem: The struct ttm_resource indicating to what memory
  *       region the move is taking place.
  *