feat: add clear cache cmd to /proc/fs_cache

write "clear pathcahe" to clear pathcaches and vnodes
write "clear pagecache" to clear pagecaches
write "clear all" to clear both pathcaches and pagechaches
the cache in use will not be cleared

close: #I3XLPH

Signed-off-by: mucor <mucorwang@gmail.com>

kernel/base/include/los_vm_filemap.h

@@ -208,6 +208,7 @@ typedef struct ProcessCB LosProcessCB;
 VOID OsVmmFileRegionFree(struct file *filep, LosProcessCB *processCB);
 #ifdef LOSCFG_DEBUG_VERSION
 VOID ResetPageCacheHitInfo(int *try, int *hit);
+struct file_map* GetFileMappingList(void);
 #endif
 #ifdef __cplusplus
 #if __cplusplus