drm/amd/display: Fix MST physical ports always disconnected

Remove a false assumption that a cached EDID will be present whenever
the connector is in a connected state as this will only be true for
logical MST ports. For physical ports the EDID will never be cached,
which will cause them to always appear as disconnected.

This reverts commit 4ff8a88888de271bfb7750b2a5c68163848e2bf1
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>