HAL: eoss3_dev: add missing __cplusplus handling

Close out the `extern "C"` definition at the top of the file when C++
is enabled.

Signed-off-by: Jordan Yates <jordan@embeint.com>

Author: JordanYates

HAL/inc/eoss3_dev.h

@@ -2463,5 +2463,9 @@ typedef struct
 #define REBOOT_CAUSE		(0xF)
 #define REBOOT_STATUS_REG	(PMU->MISC_POR_3)
 
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
 #endif /* __EOSS3_DEV_H */