musb: sunxi: switch to the device model

The device model was implemented so far using a hook that needed to be
called from the board support, without DT support and only for the host.

Switch to probing both in peripheral and host mode through the DT.

Reviewed-by: Łukasz Majewski <lukma@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>