USB: EHCI: ehci-mv: switch the HSIC HCI to HSIC mode

Turns out the undocumented and reserved bits of port status/control
register of the root port need to be set to use the HCI in HSIC mode.

Typically the firmware does this, but that is not always good enough,
because the bits get lost if the HSIC clock is disabled (e.g. when
ehci-mv is build as a module).

This supplements commit 7b104f89

 ("USB: EHCI: ehci-mv: add HSIC
support").

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20200309130014.548168-1-lkundrak@v3.sk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>