Silicon/Broadcom/BcmGenetDxe: Add GENET driver

Add support for the Broadcom GENET v5 ethernet controller
for the Raspberry Pi 4 (BCM2711)

Co-authored-by: Jared McNeill <jmcneill@invisible.ca>
Co-authored-by: Andrei Warkentin <awarkentin@vmware.com>
Co-authored-by: Samer El-Haj-Mahmoud <samer.el-haj-mahmoud@arm.com>
Co-authored-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>