net: disable MBEDTLS in SPL

Building SPL fails with MBEDTLS enabled.
Currently we don't need it there.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
diff --git a/lib/lwip/Makefile b/lib/lwip/Makefile
index 19e5c68..fe2b64c 100644
--- a/lib/lwip/Makefile
+++ b/lib/lwip/Makefile
@@ -54,5 +54,5 @@
 	lwip/src/core/udp.o \
 	lwip/src/netif/ethernet.o
 
-obj-$(CONFIG_MBEDTLS_LIB_TLS) += lwip/src/apps/altcp_tls/altcp_tls_mbedtls.o \
+obj-$(CONFIG_$(XPL_)MBEDTLS_LIB_TLS) += lwip/src/apps/altcp_tls/altcp_tls_mbedtls.o \
 	lwip/src/apps/altcp_tls/altcp_tls_mbedtls_mem.o
diff --git a/lib/lwip/u-boot/lwipopts.h b/lib/lwip/u-boot/lwipopts.h
index 88d6faf..edac74f 100644
--- a/lib/lwip/u-boot/lwipopts.h
+++ b/lib/lwip/u-boot/lwipopts.h
@@ -5,6 +5,8 @@
 #ifndef LWIP_UBOOT_LWIPOPTS_H
 #define LWIP_UBOOT_LWIPOPTS_H
 
+#include <linux/kconfig.h>
+
 #if defined(CONFIG_LWIP_DEBUG)
 #define LWIP_DEBUG 1
 #define LWIP_DBG_MIN_LEVEL              LWIP_DBG_LEVEL_ALL
@@ -154,7 +156,7 @@
 #define MEMP_MEM_INIT			1
 #define MEM_LIBC_MALLOC			1
 
-#if defined(CONFIG_MBEDTLS_LIB_TLS)
+#if CONFIG_IS_ENABLED(MBEDTLS_LIB_TLS)
 #define LWIP_ALTCP                      1
 #define LWIP_ALTCP_TLS                  1
 #define LWIP_ALTCP_TLS_MBEDTLS          1