stm32mp1: Move config SYS_MALLOC_LEN to Kconfig

This patch moves the the config SYS_MALLOC_LEN to
Kconfig as it is already done for zynq arch in
commit 01aa5b8f0503 ("Kconfig: Move config
SYS_MALLOC_LEN to Kconfig for zynq")

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/Kconfig b/Kconfig
index 5f5c5cc..fcde0c3 100644
--- a/Kconfig
+++ b/Kconfig
@@ -147,7 +147,7 @@
 
 config SYS_MALLOC_LEN
 	hex "Define memory for Dynamic allocation"
-	depends on ARCH_ZYNQ || ARCH_VERSAL
+	depends on ARCH_ZYNQ || ARCH_VERSAL || ARCH_STM32MP
 	help
 	  This defines memory to be allocated for Dynamic allocation
 	  TODO: Use for other architectures