ARM: dts: realview: DT support for the PBA8 and PBX-A9

This adds a devicetree for the ARM RealView PBA8 platform,
also known as HBI-0178, "RealView Platform Baseboard for
Cortex-A8" and PBX-A9 "RealView Platform Baseboard
Explore for Cortex-A9"

Tested in QEMU with -M realview-pb-a8, as well as with
-M realview-pbx-a9 -smp cpus=2

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Tested-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>