USB: EHCI: make ehci-mv a separate driver

This is done do that it could be enabled alongside other platform EHCI
glue drivers on multiplatform kernels.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>