Move bootloader_hal.h to the openlcb directory. (#821)

Cleans up conditional compilation.

This would normally create breakages in applications that depend on openmrn, so we leave behind a symlink.

===

* Move bootlaoder_hal.h to the openlcb directory.
Clean up conditional compilation.

* Adds symlink for backwards compatibility.

include/freertos/bootloader_hal.h

@@ -0,0 +1 @@
+../../src/openlcb/bootloader_hal.h

src/openlcb/ApplicationChecksum.hxx

@@ -35,11 +35,7 @@
 #ifndef _OPENLCB_APPLICATIONCHECKSUM_HXX_
 #define _OPENLCB_APPLICATIONCHECKSUM_HXX_
 
-#ifdef ESP_PLATFORM
-#include "bootloader_hal.h"
-#else
-#include "freertos/bootloader_hal.h"
-#endif
+#include "openlcb/bootloader_hal.h"
 
 extern "C" {
 /** @returns true if the application checksum currently in flash is correct. */

src/openlcb/Bootloader.hxx

@@ -43,16 +43,12 @@
 #include <string.h>
 #include <unistd.h>
 
-#ifdef ESP_PLATFORM
-#include "bootloader_hal.h"
-#else
-#include "freertos/bootloader_hal.h"
-#endif
-#include "openlcb/Defs.hxx"
+#include "openlcb/ApplicationChecksum.hxx"
 #include "openlcb/CanDefs.hxx"
 #include "openlcb/DatagramDefs.hxx"
+#include "openlcb/Defs.hxx"
 #include "openlcb/MemoryConfig.hxx"
-#include "openlcb/ApplicationChecksum.hxx"
+#include "openlcb/bootloader_hal.h"
 #include "can_frame.h"
 
 namespace openlcb