drm: Introduce epoch counter to drm_connector

This counter will be used by drm_helper_probe_detect caller to determine
if anything had changed(including edid, connection status and etc).
Hardware specific driver detect hooks are responsible for updating this
counter when some change is detected to notify the drm part,
which can trigger for example hotplug event.

Also now call drm_connector_update_edid_property
right after we get edid always to make sure there is a
unified way to handle edid change, without having to
change tons of source code as currently
drm_connector_update_edid_property is called only in
certain cases like reprobing and not right after edid is
actually updated.

v2: Added documentation for the new counter. Rename change_counter to
    epoch_counter.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105540

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200630002700.5451-3-kunal1.joshi@intel.com