drm: Use new mode_valid() helpers in connector probe helper

This changes the connector probe helper function to use the new
encoder->mode_valid(), bridge->mode_valid() and crtc->mode_valid()
helper callbacks to validate the modes.

The new callbacks are optional so the behaviour remains the same
if they are not implemented. If they are, then the code loops
through all the connector's encodersXbridgesXcrtcs and calls the
callback.

If at least a valid encoderXbridgeXcrtc combination is found which
accepts the mode then the function returns MODE_OK.

Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Carlos Palminha <palminha@synopsys.com>
Cc: Dave Airlie <airlied@linux.ie>
Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Changes v3->v4:
	- Change function name (Laurent)
Changes v2->v3:
	- Call also bridge->mode_valid (Daniel)
Changes v1->v2:
	- Use new helpers suggested by Ville
	- Change documentation (Daniel)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/d4e3ba87d822fa92f1b8773e441b9a02af3bde71.1495720737.git.joabreu@synopsys.com