usb: chipidea: add host role

This adds EHCI host support to the chipidea driver. We want it to be
part of the hdrc driver and not a standalone (sub-)driver module, as
the structure of ehci-hcd.c suggests, so for chipidea controller we
hack it to not provide platform-related code, but only the ehci hcd.

The ehci-platform driver won't work for us here too, because the
controller uses the same registers for both device and host mode and
also otg-related bits, so it's not really possible to put ehci registers
into a separate resource.

This is not a pretty solution, but the alternative is exporting symbols
from the chipidea driver to a ehci-chipidea driver and doing all the
module refcounting.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>