fbdev: Handle video= parameter in video/cmdline.c

fbdev: Handle video= parameter in video/cmdline.c

Handle the command-line parameter video= in video/cmdline.c. Implement
the fbdev helper fb_get_options() on top. Will allows to handle the
kernel parameter in DRM without fbdev dependencies.

Note that __video_get_options() has the meaning of its return value
inverted compared to fb_get_options(). The new helper returns true if
the adapter has been enabled, and false otherwise.

There is the ofonly parameter, which disables output for non-OF-based
framebuffers. It is only for offb and looks like a workaround. The actual
purpose it not clear to me. Use 'video=off' or 'nomodeset' instead.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230209135509.7786-9-tzimmermann@suse.de