target/loongarch: Log I/O write accesses to CSR registers

Various CSR registers have Read/Write fields. We might
want to see guest trying to change such registers.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20230821125959.28666-2-philmd@linaro.org>
Signed-off-by: Song Gao <gaosong@loongson.cn>

target/loongarch/cpu.c

@@ -544,6 +544,8 @@ static void loongarch_cpu_realizefn(DeviceState *dev, Error **errp)
 static void loongarch_qemu_write(void *opaque, hwaddr addr,
                                  uint64_t val, unsigned size)
 {
+    qemu_log_mask(LOG_UNIMP, "[%s]: Unimplemented reg 0x%" HWADDR_PRIx "\n",
+                  __func__, addr);
 }
 
 static uint64_t loongarch_qemu_read(void *opaque, hwaddr addr, unsigned size)