Convert CONFIG_SYS_MALLOC_LEN to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_MALLOC_LEN

Signed-off-by: Tom Rini <trini@konsulko.com>
Acked-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/configs/imx6dl_mamoj_defconfig b/configs/imx6dl_mamoj_defconfig
index 466f194..70268d0 100644
--- a/configs/imx6dl_mamoj_defconfig
+++ b/configs/imx6dl_mamoj_defconfig
@@ -8,6 +8,7 @@
 CONFIG_ENV_OFFSET=0x100000
 CONFIG_MX6QDL=y
 CONFIG_TARGET_MX6DL_MAMOJ=y
+CONFIG_SYS_MALLOC_LEN=0x2300000
 CONFIG_DEFAULT_DEVICE_TREE="imx6dl-mamoj"
 CONFIG_SPL_TEXT_BASE=0x00908000
 CONFIG_IMX_HAB=y