Add some additional information (input vs. output port, sink associated
with VC, peer device type, max number of VCs supported) and ensure that
any embedded '\0' characters in a branch device's devid string are not
written to debugfs.

v2: Rebase + change drm_edid_get_monitor_name() call to reflect new
    signature.

v3: Minor changes suggested by Jani + rebase.

v4: Rebase

cc: dri-devel@lists.freedesktop.org
cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jim Bride <jim.bride@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1460654317-31288-2-git-send-email-jim.bride@linux.intel.com