[TF-M] ITS File System Enhancement

Hi,

I created patches to add the XOR checksum of the whole metadata into the ITS metadata_block header. This is to check the possible error in the flash. It can happen that the ITS file system is upgraded to the new one while the ITS assets are maintained with the current ITS file system. To support compatibility with the current ITS filesystem version, at the initialization of the file system, the file metadata and the block metadata, together with the metadata_block_header are updated to the new ITS file system. The patches are: https://review.trustedfirmware.org/q/topic:%22ITS_FILESYSTEM%22+(status:open...)

Would you like to review the patches? Any comments are welcomed!

Regards, Sherry Z