fix(stm32mp2): add missing include

Without #include <plat/common/platform.h>, we have the following warning
with sparse:
plat/st/stm32mp2/bl2_plat_setup.c:15:6: warning: symbol
 'bl2_el3_early_platform_setup' was not declared. Should it be static?
plat/st/stm32mp2/bl2_plat_setup.c:23:6: warning: symbol
 'bl2_platform_setup' was not declared. Should it be static?
plat/st/stm32mp2/bl2_plat_setup.c:27:6: warning: symbol
 'bl2_el3_plat_arch_setup' was not declared. Should it be static?

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I18f9265c1eef1f8e8e0eac3d6c37a959e5c9e8b6
diff --git a/plat/st/stm32mp2/bl2_plat_setup.c b/plat/st/stm32mp2/bl2_plat_setup.c
index 0805756..5f05f63 100644
--- a/plat/st/stm32mp2/bl2_plat_setup.c
+++ b/plat/st/stm32mp2/bl2_plat_setup.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, STMicroelectronics - All Rights Reserved
+ * Copyright (c) 2023-2024, STMicroelectronics - All Rights Reserved
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -7,6 +7,8 @@
 #include <cdefs.h>
 #include <stdint.h>
 
+#include <plat/common/platform.h>
+
 #include <stm32mp_common.h>
 
 void bl2_el3_early_platform_setup(u_register_t arg0 __unused,