Adjust more modules to new design

Add `ecp.h` anf `timing.h` to new XXX_alt design
diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index d8c6823..fe34614 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -39,6 +39,10 @@
 #define MBEDTLS_ERR_ECP_SIG_LEN_MISMATCH                  -0x4C00  /**< Signature is valid but shorter than the user-supplied length. */
 #define MBEDTLS_ERR_ECP_HW_ACCEL_FAILED                   -0x4B80  /**< ECP hardware accelerator failed. */
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #if !defined(MBEDTLS_ECP_ALT)
 /*
  * default mbed TLS elliptic curve arithmetic implementation
@@ -48,10 +52,6 @@
  * one.)
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * Domain parameters (curve, subgroup and generator) identifiers.
  *
@@ -237,6 +237,10 @@
 #define MBEDTLS_ECP_PF_UNCOMPRESSED    0   /**< Uncompressed point format */
 #define MBEDTLS_ECP_PF_COMPRESSED      1   /**< Compressed point format */
 
+#else  /* MBEDTLS_ECP_ALT */
+#include "ecp_alt.h"
+#endif /* MBEDTLS_ECP_ALT */
+
 /*
  * Some other constants from RFC 4492
  */
@@ -679,8 +683,4 @@
 }
 #endif
 
-#else  /* MBEDTLS_ECP_ALT */
-#include "ecp_alt.h"
-#endif /* MBEDTLS_ECP_ALT */
-
 #endif /* ecp.h */