add 64 bit cva6 test

Author: grg-haas

.github/workflows/test-system.yml

@@ -8,12 +8,15 @@ jobs:
     environment: ${{ matrix.platform != 'generic' && 'track' || null }}
     strategy:
       matrix:
-        platform: [generic, mpfs] #cva6]
+        platform: [generic, mpfs, cva6]
         bits: [32, 64]
         exclude:
           # mpfs is not 32 bit
           - platform: mpfs
             bits: 32
+          # ignore 32-bit cva6 for now
+          - platform: cva6
+            bits: 32
 
     steps:
     - name: Checkout Keystone