drm/amdgpu/display: disable eDP fast boot optimization on DCE8

Seems to cause blank screens.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=106940


Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>