dev-arm: Don't panic when EOIR a non active PPI

GIC architecture specification says that writing EOIR with
a not active irq it is an unpredictable behavior.
So, just warn when it happens for a PPI case, like it is
already done in SPI case.

Change-Id: Icb1b8f5690d5e87b15c3b0fe2ca0d37fdd4085ee
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/13556
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
diff --git a/src/dev/arm/gic_v2.cc b/src/dev/arm/gic_v2.cc
index a24e563..293c72f 100644
--- a/src/dev/arm/gic_v2.cc
+++ b/src/dev/arm/gic_v2.cc
@@ -601,7 +601,7 @@
         } else if (iar.ack_id < (SGI_MAX + PPI_MAX) ) {
             uint32_t int_num = 1 << (iar.ack_id - SGI_MAX);
             if (!(cpuPpiActive[ctx] & int_num))
-                panic("CPU %d Done handling a PPI interrupt "
+                warn("CPU %d Done handling a PPI interrupt "
                       "that isn't active?\n", ctx);
             cpuPpiActive[ctx] &= ~int_num;
         } else {