configs: verdin-imx8mp: Fix wrong early malloc() heap size

Set, previously unset, CONFIG_SPL_SYS_MALLOC_F_LEN to 0x4000 whose
default value is 0x10000.
Early malloc() uses CRAM_S at 0x184000 (CFG_MALLOC_F_ADDR), this ram
area end at 0x188000.

Fixes: 2bc2f817cea7 ("board: toradex: add verdin imx8m plus support")
Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
diff --git a/configs/verdin-imx8mp_defconfig b/configs/verdin-imx8mp_defconfig
index 359e51a..4efe6f9 100644
--- a/configs/verdin-imx8mp_defconfig
+++ b/configs/verdin-imx8mp_defconfig
@@ -50,6 +50,7 @@
 CONFIG_SPL_BOOTROM_SUPPORT=y
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 # CONFIG_SPL_SHARES_INIT_SP_ADDR is not set
+CONFIG_SPL_SYS_MALLOC_F_LEN=0x4000
 CONFIG_SYS_SPL_MALLOC=y
 CONFIG_HAS_CUSTOM_SPL_MALLOC_START=y
 CONFIG_CUSTOM_SYS_SPL_MALLOC_ADDR=0x42200000