Include platform.h unconditionally: gcm

gcm.c had a slightly different pattern for the conditional inclusion of
platform.h which didn't fit the general replacement. Simplify it manually.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/gcm.c b/library/gcm.c
index fca0c61..53275c3 100644
--- a/library/gcm.c
+++ b/library/gcm.c
@@ -32,6 +32,7 @@
 #if defined(MBEDTLS_GCM_C)
 
 #include "mbedtls/gcm.h"
+#include "mbedtls/platform.h"
 #include "mbedtls/platform_util.h"
 #include "mbedtls/error.h"
 
@@ -41,11 +42,6 @@
 #include "aesni.h"
 #endif
 
-#if defined(MBEDTLS_SELF_TEST) && defined(MBEDTLS_AES_C)
-#include "mbedtls/aes.h"
-#include "mbedtls/platform.h"
-#endif /* MBEDTLS_SELF_TEST && MBEDTLS_AES_C */
-
 #if !defined(MBEDTLS_GCM_ALT)
 
 /* Parameter validation macros */