Changed circuit_breaker to not use px4.h

The inclusion of px4.h requires C++ features not supported in the
Hexagon toolchain. The features are not required so the required
headers are used instead.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/modules/systemlib/circuit_breaker.cpp

@@ -42,7 +42,8 @@
  * parameter needs to set to the key (magic).
  */
 
-#include <px4.h>
+#include <stdint.h>
+#include <px4_defines.h>
 #include <systemlib/circuit_breaker.h>
 
 bool circuit_breaker_enabled(const char *breaker, int32_t magic)