xilinx: board: Update logic in xilinx_read_eeprom_legacy

When eeprom has random content printing random chars can stuck U-Boot.
That's why update legacy eeprom format decoding algorithm to copy only
maximum amount of chars allocated for fields.
And also print them directly from desc structure.

Previous algorithm was printing strings first directly from eeprom content
and then copy them to desc structure.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/42065fcbb1a10581f9f4f091d64b43c01fe595c6.1674573561.git.michal.simek@amd.com