feat(st): update the security based on new compatible

From the new binding, the RCC become secured based on the new
compatible. This must be done only from the secure OS initialisation.

Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Change-Id: I7f0a62f22bfcca638ddaefc9563df00f89f01653
diff --git a/plat/st/stm32mp1/stm32mp1_def.h b/plat/st/stm32mp1/stm32mp1_def.h
index 76f3585..fd12159 100644
--- a/plat/st/stm32mp1/stm32mp1_def.h
+++ b/plat/st/stm32mp1/stm32mp1_def.h
@@ -492,5 +492,6 @@
 #define DT_NVMEM_LAYOUT_COMPAT		"st,stm32-nvmem-layout"
 #define DT_PWR_COMPAT			"st,stm32mp1,pwr-reg"
 #define DT_RCC_CLK_COMPAT		"st,stm32mp1-rcc"
+#define DT_RCC_SEC_CLK_COMPAT		"st,stm32mp1-rcc-secure"
 
 #endif /* STM32MP1_DEF_H */