apic: Fix reported DFR content

IA-32 SDM, Figure 10-14: Bits 27:0 are reserved as 1.

Fixes Jailhouse hypervisor start with in-kernel irqchips off.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/intc/apic.c

@@ -698,7 +698,7 @@ static uint32_t apic_mem_readl(void *opaque, hwaddr addr)
         val = s->log_dest << 24;
         break;
     case 0x0e:
-        val = s->dest_mode << 28;
+        val = (s->dest_mode << 28) | 0xfffffff;
         break;
     case 0x0f:
         val = s->spurious_vec;