mxs: Make ehci-mxs multiport capable

mxs: Make ehci-mxs multiport capable

Rework ehci-mxs so it supports both ports on MX28. It was necessary
to wrap the per-port configuration into struct ehci_mxs_port and pull
out the clock configuration function.

Signed-off-by: Marek Vasut <[email protected]>
Cc: Fabio Estevam <[email protected]>
Cc: Otavio Salvador <[email protected]>
Cc: Stefano Babic <[email protected]>