phy: qcom: qmp-combo: switch to DRM_AUX_BRIDGE

Switch to using the new DRM_AUX_BRIDGE helper to create the
transparent DRM bridge device instead of handcoding corresponding
functionality.

Acked-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>