Take Cryptographic API outside the XXX_ALT check

The cryptographic API should not be related to whether or not
there is alternative implementation. The API should be same for regular
implementation, and for alternative implementation, so it is defined
outside of the XXX_ALT precompilation check in the cryptographic API header
diff --git a/include/mbedtls/sha256.h b/include/mbedtls/sha256.h
index ffb16c2..8d7a1f7 100644
--- a/include/mbedtls/sha256.h
+++ b/include/mbedtls/sha256.h
@@ -35,14 +35,14 @@
 
 #define MBEDTLS_ERR_SHA256_HW_ACCEL_FAILED                -0x0037  /**< SHA-256 hardware accelerator failed */
 
-#if !defined(MBEDTLS_SHA256_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_SHA256_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          The SHA-256 context structure.
  *
@@ -61,6 +61,10 @@
 }
 mbedtls_sha256_context;
 
+#else  /* MBEDTLS_SHA256_ALT */
+#include "sha256_alt.h"
+#endif /* MBEDTLS_SHA256_ALT */
+
 /**
  * \brief          This function initializes a SHA-256 context.
  *
@@ -196,17 +200,6 @@
 
 #undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_SHA256_ALT */
-#include "sha256_alt.h"
-#endif /* MBEDTLS_SHA256_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
 
 /**
  * \brief          This function calculates the SHA-224 or SHA-256