GICv3 vGIC system registers not initialized on ARM Cortex-A15
Description of problem:
For Cortex-A15, the GICv3 vGIC registers are not initialized like for AArch64 CPUs, for example Cotex-A35, Cortex-A55, etc
Steps to reproduce:
The setup is not trivial. I can provide a boot image on request. But I hope the problem is straight-forward.
Additional information:
Suggested fix:
```diff
index 20c2737f17..136b513bda 100644
--- a/target/arm/tcg/cpu32.c
+++ b/target/arm/tcg/cpu32.c
@@ -569,6 +569,12 @@ static void cortex_a15_initfn(Object *obj)
     cpu->ccsidr[1] = 0x201fe00a; /* 32K L1 icache */
     cpu->ccsidr[2] = 0x711fe07a; /* 4096K L2 unified cache */
     cpu->isar.reset_pmcr_el0 = 0x410F3000;
+
+    /* From B3.5 VGIC Type register */
+    cpu->gic_num_lrs = 4;
+    cpu->gic_vpribits = 5;
+    cpu->gic_vprebits = 5;
+
     define_arm_cp_regs(cpu, cortexa15_cp_reginfo);
 }

```