Unconditionally add fixed mode to probed modes even if EDID is present
and has modes. Prepare for cases where the fixed mode is not present in
EDID (such as eDP MSO).

Cc: Nischal Varide <nischal.varide@intel.com>
Reviewed-by: NUma Shankar <uma.shankar@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/6979f123f3e4ed948333f1b181202bbced3c3e85.1613054234.git.jani.nikula@intel.com