resolve stricter warnings

In order to convert this repository to Meson, we need to make it
compile under `warning_level=3`.  Fix a number of warning classes
across the repository or disable them.

Some fixes are:

* Add missing header files.
* Fully initialize structs as necessary.
* Add `__attribute__((unused))` on parameters as necessary.
* Fix comparisons between signed and unsigned.
* Fix printf specifiers as necessary.
* Avoid case-fallthrough.
* Remove if conditions which are always true.

Some warnings would require extensive code changes, due to their
pervasive use, and so are disabled at a per-file level:
* `-Wpointer-arith`
* `-Wunused-result`

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: If8992b9108f12b39f796ed090ba29868c9f3c627
diff --git a/test/system.c b/test/system.c
index 24fbcdc..babf11d 100644
--- a/test/system.c
+++ b/test/system.c
@@ -11,8 +11,7 @@
 
 #include "linux/aspeed-lpc-ctrl.h"
 
-static struct aspeed_lpc_ctrl_mapping ctrl = {
-};
+static struct aspeed_lpc_ctrl_mapping ctrl = { .size = 0 };
 
 static struct mtd_info_user mtd = {
 	.type = MTD_NORFLASH,