fw: clang-tidy and splint: New make target: check

Add clang-tidy and splint static analytics check. For now, we use only
the cert-* warnings on clang-tidy and run splint with a lot of flags
to allow more things.

Changes to silence these analytics:

- Stop returning stuff from our debug print functions. We don't check
  them anyway and we don't have any way of detecting transmission
  failure.

- Declare more things static that isn't used outside of a file.

- Change types to be more consistent, typically to size_t or
  something or to uint32_t.

hw/application_fpga/fw/tk1/assert.c

@@ -7,8 +7,8 @@
 #include "led.h"
 #include "lib.h"
 
-void assert_fail(const char *assertion, const char *file,
-		   unsigned int line, const char *function)
+void assert_fail(const char *assertion, const char *file, unsigned int line,
+		 const char *function)
 {
 	htif_puts("assert: ");
 	htif_puts(assertion);