[SeaBIOS] unbounded-writes, causes buffer overflow

[Datta manikanta sri hari Danduri]

Hi

There are a few bugs related to Buffer write operations that do not control the length of data, which may overflow. I attached a reference patch. Please make changes as needed.
If possible, assign CVE, as the content written to these buffers is tainted and coming from the user, which can lead to security risks.

Thanks
Srihari