ARM: OMAP2+: enable devtmpfs and devtmpfs automount

Since udev-182, udev no longer creates device nodes under /dev
and this has to be managed by the kernel devtmpfs filesystem.

This means that a kernel built with the current OMAP2+ config
will not boot on a system with a recent udev.

Also, it is good to have /dev automatically mounted since some
non-initramfs based setups assumes this and don't manually mount it.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Acked-by: Santosh <Shilimkar&lt;santosh.shilimkar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>