Silicon/Broadcom/Bcm283x: Add GpioLib

This library is meant to be used by Bcm283x-based platforms, such
as the Raspberry Pi, to control the GPIO port pins on said platform.

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>