ARM: vexpress: Make defconfig work again

This patch updates the Versatile Express defconfig to a level
which makes it possible to run a defconfig-ed kernel work
on the board and in QEMU with modern userspace. It does:

- update cmdline to contain "console=ttyAMA0" only
- enable devtmpfs filesystem
- enable voltage regulator support
- enable ext4 filesystem
- disable low level debug and early printk

Signed-off-by: Fathi Boudra <fathi.boudra@linaro.org>
[PM: removed DEBUG_LL - it doesn't work on qemu]
[PM: reworded the commit message]
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Olof Johansson <olof@lixom.net>