dev, arm: Initialized the iccrpr register in the GIC

The IICRPR register in the GIC is currently not being initialized when
the GIC is instantiated. Initialize to the value mandated by the
architecture specification.

src/dev/arm/gic_pl390.cc

@@ -60,6 +60,7 @@ Pl390::Pl390(const Params *p)
     itLinesLog2 = ceilLog2(itLines);
 
     for (int x = 0; x < CPU_MAX; x++) {
+        iccrpr[x] = 0xff;
         cpuEnabled[x] = false;
         cpuPriority[x] = 0xff;
         cpuBpr[x] = 0;