drm/amd: Limit seamless boot by default to APUs

A hang is reported on DCN 3.2 with seamless boot enabled.
As the benefits come from an eDP setup, limit it to only enabled
by default with APUs.

Suggested-by:  <Alexander.Deucher@amd.com>
Reported-by:  <feifei.xu@amd.com>
Closes: https://lore.kernel.org/amd-gfx/85b427f6-11ec-4249-bf6f-eadf9c375f88@amd.com/T/#m2887e919d7c01b2a4860d2261b366d22e070f309


Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>