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/synquacer_developerbox_defconfig b/configs/synquacer_developerbox_defconfig
index 510e44a..802f181 100644
--- a/configs/synquacer_developerbox_defconfig
+++ b/configs/synquacer_developerbox_defconfig
@@ -5,6 +5,7 @@
 CONFIG_ENV_SIZE=0x30000
 CONFIG_ENV_OFFSET=0x300000
 CONFIG_ENV_SECT_SIZE=0x10000
+CONFIG_SYS_MALLOC_LEN=0x1000000
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="synquacer-sc2a11-developerbox"
 CONFIG_TARGET_DEVELOPERBOX=y