usb: host: mips: sead3: USB Host controller support for SEAD-3 platform.

Add EHCI driver for MIPS SEAD-3 development platform.

Signed-off-by: Chris Dearman <chris@mips.com>
Signed-off-by: Steven J. Hill <sjhill@mips.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>