board/qemu/ppc-mpc8544ds: apply Debian patch fixing wrong mcpu

board/qemu/ppc-mpc8544ds: apply Debian patch fixing wrong mcpu

When building the linux kernel for PPC_85xx cpus with GCC 8, the build fail with:

  powerpc-e500v2-linux-gnuspe-gcc: error: unrecognized argument in option '-mcpu=powerpc'
  powerpc-e500v2-linux-gnuspe-gcc: note: valid arguments to '-mcpu=' are: 8540 8548 native

"GCC started treating "PowerPC" and "PowerPC SPE" as two different architectures and
that's the reason for the reduced -mcpu list." [1]

As suggested in the crosstool-ng issue [1], apply the Debian patch to avoid
-mcpu=powerpc or -mcpu=powerpc64.

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/830981654

[1] https://github.com/crosstool-ng/crosstool-ng/issues/1152
[2] https://salsa.debian.org/kernel-team/linux/-/blob/buster/debian/patches/bugfix/powerpc/powerpc-fix-mcpu-options-for-spe-only-compiler.patch

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>