tools: acrn-crashlog: add more functions to file system utils

More file system operations for acrn-crashlog.

Signed-off-by: Liu Xinwu <xinwu.liu@intel.com>
Signed-off-by: CHEN Gang <gang.c.chen@intel.com>
Reviewed-by: Zhang Yanmin <yanmin.zhang@intel.com>
Reviewed-by: Liu Chuansheng <chuansheng.liu@intel.com>
Reviewed-by: Zhao Yakui <yakui.zhao@intel.com>
Reviewed-by: Geoffroy Van Cutsem <geoffroy.vancutsem@intel.com>
Acked-by: Eddie Dong <Eddie.dong@intel.com>

Author: lauxinw