ppc: Do not take exceptions on unknown SPRs in privileged mode

The architecture specifies that mtspr/mfspr on an unknown SPR number should act as a nop in privileged mode.

I haven't removed the warning however as it can be useful for diagnosing.

---
 target-ppc/translate.c | 11 +++++++++--

 1 file changed, 9 insertions(+), 2 deletions(-)

index a3de142..dd0ecc8 100644
@@ -4351,7 +4351,10 @@ static inline void gen_op_mfspr(DisasContext *ctx)

             qemu_log("Trying to read invalid spr %d (0x%03x) at " TARGET_FMT_lx "\n", sprn, sprn, ctx->nip - 4); }
-        gen_inval_exception(ctx, POWERPC_EXCP_INVAL_SPR);
+        /* Only generate an exception in user space, otherwise this is a nop */ +        if (ctx->pr) {
+            gen_inval_exception(ctx, POWERPC_EXCP_INVAL_SPR);
+        }
     }
 }

@@ -4503,7 +4506,11 @@ static void gen_mtspr(DisasContext *ctx)
         }
         fprintf(stderr, "Trying to write invalid spr %d (0x%03x) at " TARGET_FMT_lx "\n", sprn, sprn, ctx->nip - 4);
-        gen_inval_exception(ctx, POWERPC_EXCP_INVAL_SPR);
+
+        /* Only generate an exception in user space, otherwise this is a nop */ +        if (ctx->pr) {
+            gen_inval_exception(ctx, POWERPC_EXCP_INVAL_SPR);
+        }
     }
 }