drm/modes: Add initializer macro DRM_MODE_INIT()

The macro DRM_MODE_INIT() initializes an instance of
struct drm_display_mode with typical parameters. Convert simpledrm
and also update the macro DRM_SIMPLE_MODE().

v3:
	* fix DRM_MODE_INIT() docs (kernel test robot)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220905141648.22013-4-tzimmermann@suse.de