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/s5p_goni_defconfig b/configs/s5p_goni_defconfig
index 5865fde..1783bec 100644
--- a/configs/s5p_goni_defconfig
+++ b/configs/s5p_goni_defconfig
@@ -5,6 +5,7 @@
 CONFIG_NR_DRAM_BANKS=3
 CONFIG_ENV_SIZE=0x1000
 CONFIG_ENV_OFFSET=0x7000
+CONFIG_SYS_MALLOC_LEN=0x5001000
 CONFIG_DEFAULT_DEVICE_TREE="s5pc1xx-goni"
 CONFIG_TARGET_S5P_GONI=y
 CONFIG_ENV_VARS_UBOOT_CONFIG=y