powerpc: MSR_ILE bit must not be restored in rfi
Description of problem:
On processors that implement the MSR_ILE bit (that is, G4 and prior), the MSR_ILE bit is not restored by the `rfi` instruction.

qemu, however, does restore this bit from `srr1`.

Some ppcel operating systems rely on MSR_ILE not being restored by `rfi`, for example, Windows NT when taking a syscall.
Additional information:
Patch provided: [rfi_msr_ile.patch](/uploads/aa661fc8bcbb47585ff63f8e4ebb38ba/rfi_msr_ile.patch)

The correct behaviour for G4 and prior is performed for later processors too. Given PPC970 and later have that bit documented as reserved, this should not be a problem.