drm/amdgpu/dce6: disable hpd on local panels

Otherwise we can get a hotplug interrupt storm when
we turn the panel off if hpd interrupts were enabled
by the bios.

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=97471



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>