Platform/RaspberryPi/RPi3: Add USB host driver

The Raspberry Pi 3 uses a dedicated Synopsys DesignWare USB Host driver
to interface with various USB peripherals, including the onboard NIC.
This driver, which is based on the Android OpenPlatformPkg implementation,
provides support for that.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Pete Batard <pete@akeo.ie>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Jeremy Linton <jeremy.linton@arm.com>