drm/radeon/kms: handle !force case in connector detect more gracefully

When force == false, we don't do load detection in the connector
detect functions.  Unforunately, we also return the previous
connector state so we never get disconnect events for DVI-I, DVI-A,
or VGA.  Save whether we detected the monitor via load detection
previously and use that to determine whether we return the previous
state or not.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=41561



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>