configs/*imxrt10*: SYS_MALLOC_LEN is too large

1M of heap is more than internal ram making booting without SDRAM not
possible now it is 256k

Signed-off-by: Jesse Taube <Mr.Bossman075@gmail.com>
diff --git a/configs/imxrt1020-evk_defconfig b/configs/imxrt1020-evk_defconfig
index 5bef665..3c490bf 100644
--- a/configs/imxrt1020-evk_defconfig
+++ b/configs/imxrt1020-evk_defconfig
@@ -1,7 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_IMXRT=y
 CONFIG_SYS_TEXT_BASE=0x80002000
-CONFIG_SYS_MALLOC_LEN=0x100000
+CONFIG_SYS_MALLOC_LEN=0x40000
 CONFIG_SYS_MALLOC_F_LEN=0x8000
 CONFIG_SPL_GPIO=y
 CONFIG_SPL_LIBCOMMON_SUPPORT=y