drm/amd/display: add a no_hpd link_encoder_funcs variant

drm/amd/display: add a no_hpd link_encoder_funcs variant

For link encoders without HPD (analog or LVDS), add a
link_encoder_funcs structure with no hpd enable callbacks.

The enable and disable hpd callbacks are currently not used
outside of a special case in debugfs which checks if the hpd
is valid before using it, but this will protect us if they
ever are.

Reviewed-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>