c++: Add extern "C" { } block to header files

Adds extern "C" { } blocks to header files so that they can be
safely used by C++ source files.

Change-Id: Ia4db0c36a5dac5d3de351184a297d2af0df64532
Signed-off-by: Peter Mitsis <peter.mitsis@windriver.com>

include/init.h

@@ -21,6 +21,10 @@
 #include <device.h>
 #include <toolchain.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /*
  * System initialization levels. The PRIMARY and SECONDARY levels are
  * executed in the kernel's initialization context, which uses the interrupt
@@ -116,4 +120,8 @@
  */
 #define SYS_GET_DEVICE(name) (&SYS_GET_DEVICE_NAME(name))
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* _INIT_H_ */