ARM: versatile: convert to multi-platform

Now that all the prerequisites are in place, we can enable Versatile
boards for multi-platform kernels.

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>