allwinner: a64: power: Make sunxi_turn_off_soc static

The function is only used in this file, and it doesn't make sense for it
to be used anywhere else.
Signed-off-by: Samuel Holland <samuel@sholland.org>
Change-Id: Iab18f082911edcdbc37ceeaff8c512be68e0cb0f

plat/allwinner/sun50i_a64/sunxi_power.c

@@ -39,7 +39,7 @@ static enum pmic_type {
  * disabled.
  * This function only cares about peripherals.
  */
-void sunxi_turn_off_soc(uint16_t socid)
+static void sunxi_turn_off_soc(uint16_t socid)
 {
 	int i;