Switch sub-1GHz band (#349)

* switch band
* extract subghz api to files

firmware/targets/api-hal-include/api-hal-subghz.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef enum {
+    RfBandIsolation = 0,
+    RfBand1 = 1,
+    RfBand2 = 2,
+    RfBand3 = 3
+} RfBand;
+
+void api_hal_rf_band_set(RfBand band);
+
+#ifdef __cplusplus
+}
+#endif

firmware/targets/api-hal-include/api-hal.h

@@ -21,5 +21,6 @@ template <unsigned int N> struct STOP_EXTERNING_ME {};
 #include "api-hal-bt.h"
 #include "api-hal-spi.h"
 #include "api-hal-flash.h"
+#include "api-hal-subghz.h"
 
 void api_hal_init();