drm/connector: Add pixel clock to cmdline mode

We'll need to get the pixel clock to generate proper display modes for
all the current named modes. Let's add it to struct drm_cmdline_mode and
fill it when parsing the named mode.

Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>
Link: https://lore.kernel.org/r/20220728-rpi-analog-tv-properties-v9-12-24b168e5bcd5@cerno.tech


Signed-off-by: Maxime Ripard <maxime@cerno.tech>