USB: host: Use usb_hcd_platform_shutdown() wherever possible

Most HCD drivers are doing the same thing in their ".shutdown" callback
so it makes sense to use the generic usb_hcd_platform_shutdown()
handler there.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>