drm/vmwgfx/vmwgfx_kms: Update worthy function headers and demote others

drm/vmwgfx/vmwgfx_kms: Update worthy function headers and demote others

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

 In file included from drivers/gpu/drm/vmwgfx/vmwgfx_kms.c:37:
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c:483: warning: Function parameter or member 'new_state' not described in 'vmw_du_cursor_plane_atomic_check'
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c:483: warning: Excess function parameter 'state' description in 'vmw_du_cursor_plane_atomic_check'
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c:1069: warning: Function parameter or member 'vfb' not described in 'vmw_framebuffer_pin'
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c:1281: warning: Function parameter or member 'dev_priv' not described in 'vmw_kms_srf_ok'
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c:1907: warning: Function parameter or member 'crtc' not described in 'vmw_get_vblank_counter'
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c:1915: warning: Function parameter or member 'crtc' not described in 'vmw_enable_vblank'
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c:1923: warning: Function parameter or member 'crtc' not described in 'vmw_disable_vblank'
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c:2131: warning: Function parameter or member 'mode' not described in 'vmw_guess_mode_timing'

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/20210115181313.3431493-21-lee.jones@linaro.org