drm/vmwgfx/vmwgfx_shader: Demote kernel-doc abuses and fix-up worthy headers

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

 drivers/gpu/drm/vmwgfx/vmwgfx_shader.c:134: warning: Function parameter or member 'res' not described in 'vmw_res_to_shader'
 drivers/gpu/drm/vmwgfx/vmwgfx_shader.c:663: warning: Function parameter or member 'base' not described in 'vmw_user_shader_base_to_res'
 drivers/gpu/drm/vmwgfx/vmwgfx_shader.c:695: warning: Function parameter or member 'p_base' not described in 'vmw_user_shader_base_release'
 drivers/gpu/drm/vmwgfx/vmwgfx_shader.c:965: warning: Function parameter or member 'dev_priv' not described in 'vmw_compat_shader_add'
 drivers/gpu/drm/vmwgfx/vmwgfx_shader.c:965: warning: Function parameter or member 'size' not described in 'vmw_compat_shader_add'
 drivers/gpu/drm/vmwgfx/vmwgfx_shader.c:965: warning: Excess function parameter 'tfile' description in 'vmw_compat_shader_add'

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/20210115181313.3431493-37-lee.jones@linaro.org