shell: rtc: add header

include/shell/rtc.h

@@ -0,0 +1,7 @@
+#pragma once
+
+struct console;
+
+void shell_date(struct console *con, const char **argv, size_t argc);
+void shell_time(struct console *con, const char **argv, size_t argc);
+void shell_set_date(struct console *con, const char **argv, size_t argc);