Remove the ARM_DEVICE_MULTIPASS option and make its effect be the default.

Multipass device attachment was tested on many arm platforms by users and
only success was reported on the arm@ mailing list. This is just the
long-delayed followup of making it the default.

Multipass attachment is necessary when using vendor-supplied FDT data,
because our devices may need to be attached in a different order than they
are described in the FDT data.