usb: misc: add USB251xB/xBi Hi-Speed Hub Controller Driver

This patch adds a driver for configuration of the Microchip USB251xB/xBi
USB 2.0 hub controller series with USB 2.0 upstream connectivity, SMBus
configuration interface and two to four USB 2.0 downstream ports.

Furthermore add myself as a maintainer for this driver.

The datasheet can be found at the manufacturers website, see [1]. All
device-tree exposed configuration features have been tested on a i.MX6
platform with a USB2512B hub.

[1] http://ww1.microchip.com/downloads/en/DeviceDoc/00001692C.pdf



Signed-off-by: Richard Leitner <richard.leitner@skidata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>