drm/bridge: analogix-anx78xx: Use bridge->mode_valid() callback

Now that we have a callback to check if bridge supports a given mode
we can use it in Analogix bridge so that we restrict the number of
probbed modes to the ones we can actually display.

Also, there is no need to use mode_fixup() callback as mode_valid()
will handle the mode validation.

Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Cc: Carlos Palminha <palminha@synopsys.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Archit Taneja <architt@codeaurora.org>
Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: David Airlie <airlied@linux.ie>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1d0ed1858ae56c827bd09cc1fa6ff4a05d1530eb.1495720737.git.joabreu@synopsys.com