fix(poplar): shutdown wdt0 before powering off

Shut down watchdog0 before panic() to avoid the system being reset by
it.

Signed-off-by: Yang Xiwen <forbidden405@foxmail.com>
Change-Id: I4982202db9252b42312bd5f0f6e0729024a157df
diff --git a/plat/hisilicon/poplar/plat_pm.c b/plat/hisilicon/poplar/plat_pm.c
index 67ebca1..df842e8 100644
--- a/plat/hisilicon/poplar/plat_pm.c
+++ b/plat/hisilicon/poplar/plat_pm.c
@@ -92,6 +92,9 @@
 static void __dead2 poplar_system_off(void)
 {
 	ERROR("Poplar System Off: operation not handled.\n");
+	/* Turn off watchdog0 before panic() */
+	mmio_write_32((uintptr_t)(HISI_WDG0_BASE + 0xc00), 0x1ACCE551);
+	mmio_write_32((uintptr_t)(HISI_WDG0_BASE + 0x8),   0x00000000);
 	panic();
 }