allwinner: call PMIC setup code

As the ATF may need to do some power initialization on Allwinner
platform with AXP PMICs, call the PMIC setup code in BL31.

Stub of PMIC setup code is added, to prevent undefined reference.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
diff --git a/plat/allwinner/common/sunxi_bl31_setup.c b/plat/allwinner/common/sunxi_bl31_setup.c
index 8ecf490..7e11cec 100644
--- a/plat/allwinner/common/sunxi_bl31_setup.c
+++ b/plat/allwinner/common/sunxi_bl31_setup.c
@@ -93,6 +93,8 @@
 
 	sunxi_security_setup();
 
+	sunxi_pmic_setup();
+
 	INFO("BL31: Platform setup done\n");
 }
 
diff --git a/plat/allwinner/common/sunxi_private.h b/plat/allwinner/common/sunxi_private.h
index e45f494..49a5c50 100644
--- a/plat/allwinner/common/sunxi_private.h
+++ b/plat/allwinner/common/sunxi_private.h
@@ -13,6 +13,8 @@
 void sunxi_disable_secondary_cpus(unsigned int primary_cpu);
 
 uint16_t sunxi_read_soc_id(void);
+
+void sunxi_pmic_setup(void);
 void sunxi_security_setup(void);
 
 #endif /* __SUNXI_PRIVATE_H__ */