nova: avoid hangs on AMD with IOMMUs

With the new usb driver #4399 and usage of the updated dde_linux lx_eml/lx_kit
approach a much higher rate of IRQ session construction/destruction and signal
handler assignment (irq->sigh) are caused. This trickles down to the kernel,
which causes an hang of the AMD IOMMUs due to not setting reserved bits
adequately. The commit fixes the root cause in the kernel and add a guard
into core's to limit such driver behaviour.

Fixes #4482

repos/base-nova/ports/nova.hash

@@ -1 +1 @@
-f5e2aa3d82dd6737422987241ebc8e17ecbf640c
+7208e091c7694c61247427715d0abef7ba8d78e3

repos/base-nova/ports/nova.port

@@ -4,7 +4,7 @@ DOWNLOADS := nova.git
 
 # r10 branch
 URL(nova) := https://github.com/alex-ab/NOVA.git
-REV(nova) := de90690dbf395a786d10c22123f37feb143a109f
+REV(nova) := 1c6acf0af8256036cdea023576e2cb0e30e7d69c
 DIR(nova) := src/kernel/nova
 
 PATCHES   := $(sort $(wildcard $(REP_DIR)/patches/*.patch))

repos/base-nova/src/core/irq_session_component.cc

@@ -107,6 +107,11 @@ void Irq_object::sigh(Signal_context_capability cap)
 	if (!_sigh_cap.valid() && !cap.valid())
 		return;
 
+	if (_sigh_cap.valid() && _sigh_cap == cap) {
+		/* avoid useless overhead, e.g. with IOMMUs enabled */
+		return;
+	}
+
 	if ((_sigh_cap.valid() && !cap.valid())) {
 		deassociate(irq_sel());
 		_sigh_cap = Signal_context_capability();