drm/modes: Fix the command line parser to take force options into account

The command line parser when it has been rewritten introduced a regression
when the only thing on the command line is an option to force the detection
of a connector (such as video=HDMI-A-1:d), which are completely valid.

It's been further broken by the support for the named modes which take
anything that is not a resolution as a named mode.

Let's fix this by running the extra command line option parser on the named
modes if they only take a single character.

Fixes: e08ab74b ("drm/modes: Rewrite the command line parser")
Reported-by: Jernej Škrabec <jernej.skrabec@gmail.com>
Reported-by: Thomas Graichen <thomas.graichen@googlemail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Tested-by: Thomas Graichen <thomas.graichen@gmail.com>
Reviewed-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190827115850.25731-2-mripard@kernel.org