drm: Introduce generic probe function for component based masters.

A lot of component based DRM drivers use a variant of the same code
as the probe function. They bind the crtc ports in the first iteration
and then scan through the child nodes and bind the encoders attached
to the remote endpoints. Factor the common code into a separate
function called drm_of_component_probe() in order to increase code
reuse.

Cc: David Airlie <airlied@linux.ie>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1445332995-11212-2-git-send-email-Liviu.Dudau@arm.com


Acked-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>