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/nsim_700_defconfig b/configs/nsim_700_defconfig
index b495ff5..3607583 100644
--- a/configs/nsim_700_defconfig
+++ b/configs/nsim_700_defconfig
@@ -2,6 +2,7 @@
 CONFIG_TARGET_NSIM=y
 CONFIG_NSIM_BOARD_CPPFLAGS="-mcpu=arc700 -mlock -mswape"
 CONFIG_SYS_TEXT_BASE=0x81000000
+CONFIG_SYS_MALLOC_LEN=0x0200000
 CONFIG_DEFAULT_DEVICE_TREE="nsim"
 CONFIG_DEBUG_UART_BASE=0xf0000000
 CONFIG_DEBUG_UART_CLOCK=70000000