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/total_compute_defconfig b/configs/total_compute_defconfig
index 63bb276..313507a 100644
--- a/configs/total_compute_defconfig
+++ b/configs/total_compute_defconfig
@@ -6,6 +6,7 @@
 CONFIG_SYS_MEMTEST_START=0x80000000
 CONFIG_SYS_MEMTEST_END=0xff000000
 CONFIG_ENV_SIZE=0x2a00000
+CONFIG_SYS_MALLOC_LEN=0x3200000
 CONFIG_DEFAULT_DEVICE_TREE="total_compute"
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_SYS_LOAD_ADDR=0x90000000