Rearrange the inclusion of curve448/curve448_lcl.h

The real cause for this change is that test/ec_internal_test.c
includes ec_lcl.h, and including curve448/curve448_lcl.h from there
doesn't work so well with compilers who always do inclusions relative
to the C file being compiled.
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8334)

crypto/ec/ec_lcl.h

@@ -15,7 +15,6 @@
 #include <openssl/bn.h>
 #include "internal/refcount.h"
 #include "internal/ec_int.h"
-#include "curve448/curve448_lcl.h"
 
 #if defined(__SUNPRO_C)
 # if __SUNPRO_C >= 0x520

crypto/ec/ecx_meth.c

@@ -15,6 +15,7 @@
 #include "internal/asn1_int.h"
 #include "internal/evp_int.h"
 #include "ec_lcl.h"
+#include "curve448/curve448_lcl.h"
 
 #define X25519_BITS          253
 #define X25519_SECURITY_BITS 128