pmdomain: mediatek: Fix build-errors

Let's add the missing header to fix the reported build-errors.

Fixes: df4e9ec ("pmdomain: mediatek: Add support for secure HWCCF infra power on")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202510231317.ZZxNaFG0-lkp@intel.com/
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: Ulf Hansson

drivers/pmdomain/mediatek/mtk-pm-domains.c

@@ -2,6 +2,7 @@
 /*
  * Copyright (c) 2020 Collabora Ltd.
  */
+#include <linux/arm-smccc.h>
 #include <linux/clk.h>
 #include <linux/clk-provider.h>
 #include <linux/init.h>