usb: mtu3: rebuild role switch flow of extcon

This is a preparation patch to plan to use the same work to
handle role switch for all three supported ways.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1623139069-8173-11-git-send-email-chunfeng.yun@mediatek.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>