cpu: Add POWER8NVL information to CPU map XML

This is yet another variation of POWER8. The PVR information comes
from arch/powerpc/kernel/cputable.c in the Linux kernel tree.

src/cpu/cpu_map.xml

@@ -1372,6 +1372,7 @@
     <model name='POWER8'>
       <vendor name='IBM'/>
       <pvr value='0x004b0000' mask='0xffff0000'/>
+      <pvr value='0x004c0000' mask='0xffff0000'/>
       <pvr value='0x004d0000' mask='0xffff0000'/>
     </model>