Rework selection of architecture / machine selection

[andreasf]

Currently there is one list with combinations of architecture and emulated board/machine.

This list is incomplete for QEMU CVS and is potentially growing. Also, this selection has effects on the other options available.

Suggestion: Reorder controls hierarchically so that the architecture selection is on the top and influences the selection of machines (possibly retrieve options automatically via "-M ?" overriding known options). The combination of architecture and machine should then influence other available options.

Examples:

• The Sparc32 SS-5 machine [renamed in post-0.9.0] does not allow more than 256 MB RAM. In any case, Q should catch such error messages of an exiting QEMU and display them in a sheet so that the user knows. Then, following this suggestion the Edit PC GUI could be made aware of this and limit the RAM size to numbers known valid (manually).
• The default Sparc32 "-net nic" network device is not NE2000 but Lance (pcnet). Either label the current NE2000 option "Default" or name it correctly based on arch+machine to avoid confusion.
• Disable or hide pcnet and Realtek for Sparc32 (not available).

Such differences between machines appear to be quite common, depending on implementation progress or real hardware.