USB: enclose EHCI HCD drivers within an if USB_EHCI_HCD block

Thist patch removes the depends on USB_EHCI_HCD that the various USB
EHCI HCD drivers use and encloses every driver within an if USB_EHCI_HCD
/ endif block. The EHCI HCD platform and Octeon drivers have been moved
around to remain enclosed within this block.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>