gpio: Enable guard for Zephyr sources
Enable the guard that prevents Zephyr source files from including the
legacy GPIO header and API.
BRANCH=none
TEST=zmake testall
#include "common.h"
#include "console.h"
+#ifdef __REQUIRE_ZEPHYR_GPIOS__
+#error "Zephyr source files must use the Zephyr GPIO API"
+#endif
/*
* If compiling with Zephyr, include the GPIO_ definitions to deal with name
