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/include/u-boot/sha512.h b/include/u-boot/sha512.h
index 7e10f59..92660d9 100644
--- a/include/u-boot/sha512.h
+++ b/include/u-boot/sha512.h
@@ -1,9 +1,10 @@
 #ifndef _SHA512_H
 #define _SHA512_H
 
+#include <linux/kconfig.h>
 #include <linux/types.h>
 
-#if defined(CONFIG_MBEDTLS_LIB_CRYPTO)
+#if CONFIG_IS_ENABLED(MBEDTLS_LIB_CRYPTO)
 #include <mbedtls/sha512.h>
 #endif
 
@@ -16,7 +17,7 @@
 #define CHUNKSZ_SHA384	(16 * 1024)
 #define CHUNKSZ_SHA512	(16 * 1024)
 
-#if defined(CONFIG_MBEDTLS_LIB_CRYPTO)
+#if CONFIG_IS_ENABLED(MBEDTLS_LIB_CRYPTO)
 typedef mbedtls_sha512_context sha384_context;
 typedef mbedtls_sha512_context sha512_context;
 #else