drm: vc4: Use crtc->mode_valid() and encoder->mode_valid() callbacks

drm: vc4: Use crtc->mode_valid() and encoder->mode_valid() callbacks

Now that we have a callback to check if crtc and encoder supports a
given mode we can use it in vc4 so that we restrict the number of
probed modes to the ones we can actually display.

Also, remove the mode_fixup() calls as these are no longer needed
because mode_valid() will be called before.

Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Cc: Carlos Palminha <palminha@synopsys.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Eric Anholt <eric@anholt.net>
Cc: David Airlie <airlied@linux.ie>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Compile-tested and Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/5bea792f91074688c88a2dab8b0a90eec6e98fdf.1495720737.git.joabreu@synopsys.com