include: rearrange for standard use of extern "C" in various headers

Consistently place C++ use of extern "C" after all include directives,
within the negative branch of _ASMLANGUAGE if used.

The inclusion of the generated syscall files is placed outside the
extern "C" block as the generated file has its own extern "C" block.

Background from issue #17997:

Declarations that use C linkage should be placed within extern "C"
so the language linkage is correct when the header is included by
a C++ compiler.

Similarly #include directives should be outside the extern "C" to
ensure the language-specific default linkage is applied to any
declarations provided by the included header.

See: https://en.cppreference.com/w/cpp/language/language_linkage
Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>

include/device.h

@@ -596,9 +596,10 @@ static inline int device_pm_put_sync(struct device *dev) { return -ENOTSUP; }
  * @}
  */
 
-#include <syscalls/device.h>
-
 #ifdef __cplusplus
 }
 #endif
+
+#include <syscalls/device.h>
+
 #endif /* ZEPHYR_INCLUDE_DEVICE_H_ */