drm/radeon/evergreen+: don't enable HPD interrupts on eDP/LVDS

Avoids potential interrupt storms when the display is disabled.

May fix:
https://bugzilla.kernel.org/show_bug.cgi?id=56041



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org