drm/i915: Add bigjoiner force enable option to debugfs

For validation purposes, it might be useful to be able to
force Bigjoiner mode, even if current dotclock/resolution
do not require that.
Lets add such to option to debugfs.

v2: - Apparently intel_dp_need_bigjoiner can't be used, when
      debugfs entry is created so lets just check manually
      the DISPLAY_VER.

v3: - Switch to intel_connector from drm_connector(Jani Nikula)
    - Remove redundant modeset lock(Jani Nikula)
    - Use kstrtobool_from_user for boolean value(Jani Nikula)

v4: - Apply the changes to proper function(Jani Nikula)

v5: - Removed unnecessary check from i915_bigjoiner_enable_show
      (Ville Syrjälä)
    - Added eDP connector check to intel_connector_debugfs_add
      (Ville Syrjälä)
    - Removed debug message in order to prevent dmesg flooding
      (Ville Syrjälä)

v6: - Assume now always that m->private is intel_connector
    - Fixed other similar conflicts

v7: - Move bigjoiner force option to intel_connector(Ville Syrjälä)
    - Use DEFINE_SHOW_STORE_ATTRIBUTE instead of defining fops
      manually.(Ville Syrjälä)

v8: - Pass intel_connector to debugfs_create_file, instead of drm_connector.
      (Jani Nikula)

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240212125011.66174-1-uma.shankar@intel.com