refactor(stm32mp2): remove useless STM32MP_SEC_SYSRAM_SIZE

The macro STM32MP_SEC_SYSRAM_SIZE only redefine STM32MP_SYSRAM_SIZE.
Directly use the latter one and remove the STM32MP_SEC_SYSRAM_SIZE.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I9cca19fda7294be3f31ec74293ce122037541d12
diff --git a/plat/st/stm32mp2/include/platform_def.h b/plat/st/stm32mp2/include/platform_def.h
index e720c02..d3167af 100644
--- a/plat/st/stm32mp2/include/platform_def.h
+++ b/plat/st/stm32mp2/include/platform_def.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023-2024, STMicroelectronics - All Rights Reserved
+ * Copyright (c) 2023-2025, STMicroelectronics - All Rights Reserved
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -74,7 +74,7 @@
  * BL31 specific defines.
  ******************************************************************************/
 #define BL31_BASE			0
-#define BL31_LIMIT			(STM32MP_SEC_SYSRAM_SIZE / 2)
+#define BL31_LIMIT			(STM32MP_SYSRAM_SIZE / 2)
 
 /*******************************************************************************
  * BL33 specific defines.