mlxbf-bootctl: Support sysfs entries for MFG fields

mlxbf-bootctl: Support sysfs entries for MFG fields

This patch extends the mlxbf-bootctl driver's sysfs entries
to support read and write access for the manufacturing (MFG)
fields in the board-level EEPROM.  The MFG fields are set
once during the board manufacturing phase, and then the MFG
fields are write-protected.

Signed-off-by: David Thompson <davthompson@nvidia.com>
Reviewed-by: Shravan Kumar Ramani <shravankr@nvidia.com>
Link: https://lore.kernel.org/r/20230821183939.3229-1-davthompson@nvidia.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>