Before this commit it was impossible to combine an extra mode argument
specified directly after the resolution with an option, e.g.
video=HDMI-1:720x480e,rotate=180 would not work, either the "e" to force
enable would need to be dropped or the ",rotate=180", otherwise the
mode_option would not be accepted.

This commit fixes this by setting parse_extras to true in this case, so
that drm_mode_parse_cmdline_res_mode() parses the extra arguments directly
after the resolution.
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191118155134.30468-4-hdegoede@redhat.com