dev-arm: Fix GICv3 IGRPMOD writes

Writes to IGRPMOD were not right shifting the value, which resulted in
interrupts having a IGRPMOD value > 1, whereas the only allowed values
are 0 and 1.

Change-Id: Id491bd1b184d6e5abeeea25ea272eeb91792ccf7
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20613
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/src/dev/arm/gic_v3_distributor.cc b/src/dev/arm/gic_v3_distributor.cc
index bae90bf..f85474c 100644
--- a/src/dev/arm/gic_v3_distributor.cc
+++ b/src/dev/arm/gic_v3_distributor.cc
@@ -794,7 +794,7 @@
 
                 for (int i = 0, int_id = first_intid;
                      i < 8 * size && int_id < itLines; i++, int_id++) {
-                    irqGrpmod[int_id] = data & (0x1 << i);
+                    irqGrpmod[int_id] = bits(data, i);
                 }
 
                 return ;