usb: ehci: Make usage of generic_{setup,shutdown}_phy() helpers

Replace ehci_setup_phy() and ehci_shutdown_phy () by respectively
generic_setup_phy() and generic_shutdown_phy().

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Simon Glass <sjg@chromium.org>