makes LuaJit builds for mpc85xx targets with SPE ISA extension
enabled possible

Quoting inner commit message:

This allows building LuaJit for systems with Power ISA SPE
extension[^1] support by using soft float on LuaJit side.

While e500 CPU cores support SPE instruction set extension
allowing them to perform floating point arithmetic natively,
this isn't required. They can function with software floating
point to integer arithmetic translation as well,
just like FPU-less PowerPC CPUs without SPE support.

Therefore I see no need to prevent them from running LuaJit
explicitly.

[^1]: https://www.nxp.com/docs/en/reference-manual/SPEPEM.pdf

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Šimon Bořek <simon.borek@nic.cz>
(cherry picked from commit a4a484fbca)