MpactCherioCPU: fix irq handling

Restore init'd mpact_id to -1 so we can dtrt in OnGPIO and discard
irq's when no simulator is running to process them.

Change-Id: Ic615dd458e0a01ccaef9a4bacb7962d80b12750b

sencha.resc

diff --git a/sencha.resc b/sencha.resc
index ceae2c4..c491fe0 100644
--- a/sencha.resc
+++ b/sencha.resc
@@ -82,6 +82,8 @@
 i2s0 InputFile $i2s_mic_audio_file
 #i2s0 OutputFile $i2s_speaker_audio_file
 
+logLevel 0 i2s0
+
 $kelvinLibrary ?= @out/kelvin/sim/librenode_kelvin.so
 sysbus.cpu2 CpuLibraryPath $kelvinLibrary
 # Start the vector core at address 0 of its instruction TCM.

shodan_infrastructure/MpactCheriotCPU.cs

diff --git a/shodan_infrastructure/MpactCheriotCPU.cs b/shodan_infrastructure/MpactCheriotCPU.cs
index b814cd6..0f0fe46 100644
--- a/shodan_infrastructure/MpactCheriotCPU.cs
+++ b/shodan_infrastructure/MpactCheriotCPU.cs
@@ -711,7 +711,7 @@
 
 #pragma warning restore 649
 
-    private Int32 mpact_id {get; set;}
+    private Int32 mpact_id = -1;
     private ulong instructionsExecutedThisRound {get; set;}
     private ulong totalExecutedInstructions {get; set;}
     private const int PC_ID = 0x07b1;