[AT91] Add support for RSI EWS board (machine type 1609)

[Josef Holzmayr]

This adds support for the RSI EWS machine (at91rm9200-based), machine type 1609. Includes smaller cleanups as suggested by Russell and R.Schwebel. Applies cleanly to Linus' latest git, but the machine id is missing in mainlines mach-types file.

Please yell if something is wrong, inadequate, obscure.

Thanks, Josef



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