arm64: vexpress: Add dts files for the ARMv8 RTSM models

This patch adds the DTS files for the ARMv8 RTSM and Foundation models.

Signed-off-by: Pawel Moll <Pawel.Moll@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>