Power up the ASTDP connector for connection status detection if the
connector is not active. Keep it powered if a display is attached.

This fixes a bug where the connector does not come back after
disconnecting the display. The encoder's atomic_disable turns off
power on the physical connector. Further HPD reads will fail,
thus preventing the driver from detecting re-connected displays.

For connectors that are actively used, only test the HPD flag without
touching power.

Fixes: f81bb0ac ("drm/ast: report connection status on Display Port.")
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Dave Airlie <airlied@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v6.6+
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240717143319.104012-2-tzimmermann@suse.de