ARM: vexpress: Enable platform-specific options in defconfig

This patch enables all drivers and alike to make defconfig-ed
kernels use Versatile Express specific features, like power
management services (PSCI, MCPM with drivers for DCCSB on
Fast Models and SPC on TC2), CMA for frame buffer allocation,
all virtio device drivers (for QEMU, KVM tools and Fast Models),
MTD physmap drivers with squashfs and UBIFS for flash,
I2C master, regulator and hwmon drivers and LEDs support with
most useful triggers. The maximum amount of CPUs has been
increased to 8 to facilitate big.Little systems.

Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Olof Johansson <olof@lixom.net>