PPC: KVM: Make pv hcall endian agnostic

There were a few revisions of the Linux kernel that incorrectly swapped
the hcall instructions when they saw ePAPR compliant hypercalls.

We already have fixups for those in place when running with PR KVM, but
HV KVM and systems that don't implement hypercalls at all are still broken
because they fall back to the QEMU implementation of fallback hypercalls.

So let's make the fallback hypercall instruction path endian agnostic. This
only really works well for 64bit guests, but I don't think there are any 32bit
systems left that don't implement real pv hcall support, so we'll never get
into this code path.

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