hw/ppc: Reset timebase facilities on machine reset

Lower interrupts, delete timers, and set time facility registers
back to initial state on machine reset.

This is not so important for record-replay since timebase and
decrementer are migrated, but it gives a cleaner reset state.

Cc: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Cc: BALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[ clg: checkpatch.pl fixes ]
Signed-off-by: Cédric Le Goater <clg@kaod.org>

hw/ppc/prep.c

@@ -67,6 +67,7 @@ static void ppc_prep_reset(void *opaque)
     PowerPCCPU *cpu = opaque;
 
     cpu_reset(CPU(cpu));
+    cpu_ppc_tb_reset(&cpu->env);
 }