rc_input make RC_SCAN_STRING static constexpr

src/drivers/rc_input/RCInput.cpp

@@ -42,6 +42,7 @@ static bool bind_spektrum(int arg);
 #endif /* SPEKTRUM_POWER */
 
 work_s RCInput::_work = {};
+constexpr char const *RCInput::RC_SCAN_STRING[];
 
 RCInput::RCInput(bool run_as_task) :
 	_cycle_perf(perf_alloc(PC_ELAPSED, "rc_input cycle time")),

src/drivers/rc_input/RCInput.hpp

@@ -99,10 +99,9 @@ private:
 		RC_SCAN_SUMD,
 		RC_SCAN_ST24,
 		RC_SCAN_CRSF
-	};
-	enum RC_SCAN _rc_scan_state = RC_SCAN_SBUS;
+	} _rc_scan_state{RC_SCAN_SBUS};
 
-	char const *RC_SCAN_STRING[6] = {
+	static constexpr char const *RC_SCAN_STRING[6] {
 		"PPM",
 		"SBUS",
 		"DSM",