usb: musb: dsps: Call usb_phy(_shutdown/_init) during musb_platform_reset()

For DSPS platform usb_phy_vbus(_off/_on) are NOPs.
So during musb_platform_reset() call usb_phy(_shutdown/_init)

Signed-off-by: George Cherian <george.cherian@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>