misc: hisi_hikey_usb: Driver to support onboard USB gpio hub on Hikey960

The HiKey960 has a fairly complex USB configuration due to it
needing to support a USB-C port for host/device mode and multiple
USB-A ports in host mode, all using a single USB controller.

See schematics here:
  https://github.com/96boards/documentation/raw/master/consumer/hikey/hikey960/hardware-docs/HiKey960_Schematics.pdf

This driver acts as a usb-role-switch intermediary, intercepting
the role switch notifications from the tcpm code, and passing
them on to the dwc3 core.

In doing so, it also controls the onboard hub and power gpios in
order to properly route the data lines between the USB-C port
and the onboard hub to the USB-A ports.

Signed-off-by: Yu Chen <chenyu56@huawei.com>
[jstultz: Major rework to make the driver a usb-role-switch
          intermediary]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/c263f72e1d803c18c45a69ce2c333e79a7ed89ff.1599717402.git.mchehab+huawei@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>