usb: musb: Support setting OTG mode using generic PHY

When musb->xceiv is not provided but musb->phy is, support setting the
OTG mode (host, peripheral) using the generic PHY framework.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20221026182657.146630-5-paul@crapouillou.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>