Cr50: Ensure that trng.h is self-contained.

* Include trng.h from trng.c before any other header to verify that the
  header is self-contained.

* Add inclusion of stdint.h to trng.h to provide definition for uint32_t.

BUG=none
BRANCH=none
TEST=make -j buildall

Change-Id: I78fb6d915c357236ca0fed2a57f093f0eec07fe9
Reviewed-on: https://chromium-review.googlesource.com/417424
Commit-Ready: Carl Hamilton <carlh@chromium.org>
Tested-by: Carl Hamilton <carlh@chromium.org>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>

chip/g/trng.c

@@ -5,6 +5,7 @@
 
 #include "init_chip.h"
 #include "registers.h"
+#include "trng.h"
 
 void init_trng(void)
 {

include/trng.h

@@ -6,6 +6,7 @@
 #define __EC_INCLUDE_TRNG_H
 
 #include <stddef.h>
+#include <stdint.h>
 
 /**
  * Initialize the true random number generator.