MAINTAINERS: ARM Versatile Express platform

This patch adds a separate section for the ARM
Versatile Express platform maintainers, listing
all different bits and bobs used by it.

Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Acked-by: Michael Turquette <mturquette@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>