Remove Atmel AT91RM9200 and AT91SAM9 support.

[imp]

Summary

The last known robust version of this code base was FreeBSD 8.2. There
are no users of this on current, and all users of it have abandoned
this platform or are in legacy mode with a prior version of FreeBSD.

No objection on arm@.

[andrew]

I think this will also remove support for the last ARMv4 SoC.

[andrew]

In D16312#346225, @andrew wrote:

I think this will also remove support for the last ARMv4 SoC.

No, CNS11XXNAS is also ARMv4.

[imp]

In D16312#346248, @andrew wrote:

In D16312#346225, @andrew wrote:

I think this will also remove support for the last ARMv4 SoC.

No, CNS11XXNAS is also ARMv4.

We should remove that. It's had no updates since it was committed (apart from dozens of commits that were cleanup... meaning it was only costing us), the boards it ran on had 16MB, there's no bug reports for it, no questions about it in arm@ (apart from the initial here's a port message). It's been EoL'd. I don't think it even works (since the AT91RM9200 stuff has not successfully booted since FreeBSD 8 as far as we know, and it was armv4).