USB host: Add USB ehci support for nuvoton npcm7xx platform

This patch adds support for ehci controller for the Nuvoton
npcm7xx platform.
Most of the code was taken from ehci-spear.c + specific initialization
code

Signed-off-by: Avi Fishman <AviFishman70@gmail.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>