drm/ast: Fix ast_dp connection status

ast_dp_is_connected() used to also check for link training success
to report the DP connector as connected. Without this check, the
physical_status is always connected. So if no monitor is present, it
will fail to read the EDID and set the default resolution to 640x480
instead of 1024x768.

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Fixes: 22814751 ("drm/ast: astdp: Perform link training during atomic_enable")
Reported-by: Jerry Hoemann <jerry.hoemann@hpe.com>
Tested-by: Jose Lopez <jose.lopez@hpe.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Dave Airlie <airlied@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v6.12+
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20250124141142.2434138-1-jfalempe@redhat.com