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/mscc_servalt_defconfig b/configs/mscc_servalt_defconfig
index c8a9846..1530fef 100644
--- a/configs/mscc_servalt_defconfig
+++ b/configs/mscc_servalt_defconfig
@@ -6,6 +6,7 @@
 CONFIG_ENV_SIZE=0x2000
 CONFIG_ENV_OFFSET=0x100000
 CONFIG_ENV_SECT_SIZE=0x40000
+CONFIG_SYS_MALLOC_LEN=0x1f0000
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="servalt_pcb116"
 CONFIG_ENV_OFFSET_REDUND=0x140000