KVM: PPC: Book3S HV P9: Avoid SPR scoreboard stalls

Avoid interleaving mfSPR and mtSPR to reduce SPR scoreboard stalls.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-26-npiggin@gmail.com