[yocto] what's the recommended way to extend FILESOVERRIDES to add a powerpc CPU?

[Robert P. J. Day]

   currently working on a layer for building for three powerpc-based  
target boards:

   * mach1 (8260-based)
   * mach2, mach3 (8360-based)

i wanted to use FILESOVERRIDES to be able to distinguish between patches
that were:

   * machine-specific
   * CPU-specific (8260 or 8360)
   * common across all powerpc targets

however, a quick check shows me that TRANSLATED_TARGET_ARCH contains
only "powerpc", so that FILESOVERRIDES starts with:

   "powerpc:machine-name:..."

in short, with the *default* powerpc recipes, i can't define patches
that are specific to a processor, only to powerpc (redundant) or to
only a single machine.

   i can, of course, hack either of those two variables and cram an extra
field in there, but is there a *recommended* way to do this so that
i don't feel i have to take a shower afterwards?

rday