Transfer List Checksum Correction and Impact on Bloblist

[Harrison Mutai]

Hi all,

We recently applied changes to the transfer list library [1] to correct 
the checksum calculation. Previously, we used a simple byte-sum 
approach. However, we later realized this contradicts the Firmware 
Handoff specification, which states:

> The checksum is set to a value such that the XOR over every byte in the
> {tl_base_pa, …, tl_base_pa + used_size - 1} address range is equal to 0.

This discrepancy creates problems when interoperating with Bloblist.
Should Bloblist’s checksum calculation be updated to follow the same 
XOR-based method?

[1] 
https://review.trustedfirmware.org/c/shared/transfer-list-library/+/42548

All the best,
Harrison