drm/radeon: don't mess with hot plug detect for eDP or LVDS connector v2

It seems imac pannel doesn't like whe we change the hot plug setup
and then refuse to work. This help but doesn't fully fix:
https://bugzilla.redhat.com/show_bug.cgi?id=726143



v2: fix typo and improve commit message

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>