video/cmdline: Introduce CONFIG_VIDEO for video= parameter

Add CONFIG_VIDEO for common code in drivers/video/. Use the option to
select helpers for the video= parameter. Replaces CONFIG_VIDEO_CMDLINE.

Other common code in drivers/video/ can be moved behind CONFIG_VIDEO,
which will simplify the Kconfig rules.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20240118090721.7995-2-tzimmermann@suse.de