sys/kern: Add VFS support

- Refactor the libio interface

- Move syscalls into an rtemsbsd location

- Provide a root directory mount point

Update #4475

rtemsbsd/include/machine/rtems-bsd-page.h

@@ -49,6 +49,7 @@
 
 #include <sys/cdefs.h>
 #include <sys/param.h>
+
 #include <stdint.h>
 
 __BEGIN_DECLS
@@ -61,6 +62,8 @@ void *rtems_bsd_page_alloc(uintptr_t size_in_bytes, int wait);
 
 void rtems_bsd_page_free(void *addr);
 
+void vm_pager_bufferinit(void);
+
 static inline void **
 rtems_bsd_page_get_object_entry(void *addr)
 {