feat(stm32mp2): improve BL31 size management

Change the size of BL31 limit allocation to be half the sysram size.
Defining BL31_PROGBITS_LIMIT to detect overflows.

Signed-off-by: Maxime Méré <maxime.mere@foss.st.com>
Change-Id: Iccc1cc0826b8113a3c2fd6ffa77ca419795854d3
diff --git a/plat/st/stm32mp2/stm32mp2_def.h b/plat/st/stm32mp2/stm32mp2_def.h
index d3290c3..615e5c9 100644
--- a/plat/st/stm32mp2/stm32mp2_def.h
+++ b/plat/st/stm32mp2/stm32mp2_def.h
@@ -109,10 +109,12 @@
 #define STM32MP_BL2_RO_SIZE			U(0x00020000) /* 128 KB */
 #define STM32MP_BL2_SIZE			U(0x00029000) /* 164 KB for BL2 */
 
-/* Allocate remaining sysram to BL31 */
+/* Allocate remaining sysram to BL31 Binary only */
 #define STM32MP_BL31_SIZE			(STM32MP_SEC_SYSRAM_SIZE - \
 						 STM32MP_BL2_SIZE)
 
+#define BL31_PROGBITS_LIMIT			STM32MP_BL31_SIZE
+
 #define STM32MP_BL2_BASE			(STM32MP_SYSRAM_BASE + \
 						 STM32MP_SYSRAM_SIZE - \
 						 STM32MP_BL2_SIZE)