KVM: PPC: Graciously fail broken LE hypercalls

There are LE Linux guests out there that don't handle hypercalls correctly.
Instead of interpreting the instruction stream from device tree as big endian
they assume it's a little endian instruction stream and fail.

When we see an illegal instruction from such a byte reversed instruction stream,
bail out graciously and just declare every hcall as error.

Signed-off-by: Alexander Graf <agraf@suse.de>