Check for audio support by the attached sink by consulting the EDID
prior to enabling audio over the TMDS link.  We must consult the EDID
after calling drm_helper_probe_single_connector_modes(), as this can
use an override EDID, or load a replacement EDID.
Tested-by: NJon Medhurst <tixy@linaro.org>
Acked-by: NJon Medhurst <tixy@linaro.org>
Tested-by: NJyri Sarha <jsarha@ti.com>
Signed-off-by: NRussell King <rmk+kernel@armlinux.org.uk>