architecture-specific FDT devices

[Yuri Honegger <yuri.honegger%icloud.com@localhost>]

Hello,
As already discussed a few days ago, I've been trying to get FDT working with armv5. While doing so, I've run into a 
build system problem I'm not quite sure how to solve best.

In arch/arm/fdt/files.fdt, we attach a gicvthree. Unlike most other devices in files.fdt, gicvthree is defined in 
arch/arm/cortex/files.cortex. Since armv5 is pre-cortex, my GENERIC_V5 configuration doesn't include files.cortex. 
I've also noticed that many other devices in files.fdt most likely won't ever be found on an armv5 build and could be 
left out.

Therefore, I've been wondering if it is worth splitting up files.fdt into generic parts and more architecture specific 
parts. 
- If so, where would we put them? As files.fdt_cortex next to files.fdt into arch/arm/fdt/?
- Or perhaps all the way up into GENERIC / GENERIC64?
- If we don't want to split it, how can you break the gicvthree dependency described above?

For now, I've just been commenting stuff out, but that obviously won't work if this will ever get merged.

- yuri