mask all interrupts when MASTER_DISABLE is set

The MASTER_DISABLE bit (aka mask-all) masks all the interrupts.

According to Sun-4M System Architecture
"The level–15 interrupt sources [...] are maskable with the Interrupt Target
Mask Register. While these interrupts are considered ’non–maskable’ within
the SPARC IU, a mask capability is provided to allow the boot firmware
to establish a basic environment before receiving any level–15 interrupts,
which are non–maskable within SPARC. A mask–all bit is provided to allow
disabling of all external interrupts during change of the CIT."
Signed-off-by: NArtyom Tarasenko <atar4qemu@gmail.com>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

hw/slavio_intctl.c

@@ -289,9 +289,12 @@ static void slavio_check_interrupts(SLAVIO_INTCTLState *s, int set_irqs)
             }
         }
 
-        /* Level 15 and CPU timer interrupts are not maskable */
+        /* Level 15 and CPU timer interrupts are only masked when
+           the MASTER_DISABLE bit is set */
+        if (!(s->intregm_disabled & MASTER_DISABLE)) {
             pil_pending |= s->slaves[i].intreg_pending &
                 (CPU_IRQ_INT15_IN | CPU_IRQ_TIMER_IN);
+        }
 
         /* Add soft interrupts */
         pil_pending |= (s->slaves[i].intreg_pending & CPU_SOFTIRQ_MASK) >> 16;