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

 drivers/gpu/drm/vmwgfx/vmwgfx_cmdbuf.c:58: warning: Function parameter or member 'block_submission' not described in 'vmw_cmdbuf_context'
 drivers/gpu/drm/vmwgfx/vmwgfx_cmdbuf.c:109: warning: cannot understand function prototype: 'struct vmw_cmdbuf_man '
 drivers/gpu/drm/vmwgfx/vmwgfx_cmdbuf.c:164: warning: Function parameter or member 'handle' not described in 'vmw_cmdbuf_header'
 drivers/gpu/drm/vmwgfx/vmwgfx_cmdbuf.c:257: warning: Function parameter or member 'header' not described in '__vmw_cmdbuf_header_free'
 drivers/gpu/drm/vmwgfx/vmwgfx_cmdbuf.c:380: warning: Function parameter or member 'notempty' not described in 'vmw_cmdbuf_ctx_process'
 drivers/gpu/drm/vmwgfx/vmwgfx_cmdbuf.c:1168: warning: Function parameter or member 'context' not described in 'vmw_cmdbuf_preempt'
 drivers/gpu/drm/vmwgfx/vmwgfx_cmdbuf.c:1193: warning: Function parameter or member 'context' not described in 'vmw_cmdbuf_startstop'

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/20210115181313.3431493-38-lee.jones@linaro.org