usb: mtu3: add new helpers for host suspend/resume

Extract two helpers for host suspend and resume, will make it easy
to support dual-role mode suspend/resume later.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1626340078-29111-10-git-send-email-chunfeng.yun@mediatek.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>