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/mx6ull_14x14_evk_defconfig b/configs/mx6ull_14x14_evk_defconfig
index e349374..8ecb496 100644
--- a/configs/mx6ull_14x14_evk_defconfig
+++ b/configs/mx6ull_14x14_evk_defconfig
@@ -8,6 +8,7 @@
 CONFIG_ENV_OFFSET=0xC0000
 CONFIG_MX6ULL=y
 CONFIG_TARGET_MX6ULL_14X14_EVK=y
+CONFIG_SYS_MALLOC_LEN=0x1000000
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="imx6ull-14x14-evk"
 CONFIG_SUPPORT_RAW_INITRD=y