ARM: 6647/1: add Versatile Express defconfig

Being able to compile a major reference platform is helpful for
me when developing on other archs using the same e.g. PrimeCells.
I bet this is useful to others as well.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>