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/odroid-xu3_defconfig b/configs/odroid-xu3_defconfig
index deb0ce5..b243173 100644
--- a/configs/odroid-xu3_defconfig
+++ b/configs/odroid-xu3_defconfig
@@ -7,6 +7,7 @@
 CONFIG_NR_DRAM_BANKS=8
 CONFIG_ENV_SIZE=0x4000
 CONFIG_ENV_OFFSET=0x310000
+CONFIG_SYS_MALLOC_LEN=0x5004000
 CONFIG_DEFAULT_DEVICE_TREE="exynos5422-odroidxu3"
 CONFIG_IDENT_STRING=" for ODROID-XU3/XU4/HC1/HC2"
 CONFIG_DISTRO_DEFAULTS=y