stm32mp1: call regulators_enable_boot_on in board_init

U-Boot activates regulators by reading the "regulator-boot-on"
property in DT; it is requested by M4 early Boot feature.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>

board/st/stm32mp1/stm32mp1.c

@@ -515,6 +515,10 @@ int board_init(void)
 
 	board_key_check();
 
+#ifdef CONFIG_DM_REGULATOR
+	regulators_enable_boot_on(_DEBUG);
+#endif
+
 	sysconf_init();
 
 	if (IS_ENABLED(CONFIG_LED))