uhci-platform: Change compatible string from platform-uhci to generic-uhci

This brings the uhci-platform bindings in sync with what we've done for
the ohci- and ehci-platform drivers. As discussed there using platform as a
prefix is a bit weird as the platform bus is a Linux specific thing and
the bindings are supposed to be OS agnostic.

Note that the old platform-uhci compatible string is kept around for, well,
compatibility reasons.

While at it rename the bindings txt file to match the name of all the
other ?hci-platform bindings docs.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>