u-boot sys_eeprom: Add/Revise the command help messages

- Show message after executing the 'read' and 'erase' commands.
- Revise the help messages of 'usage', 'read', and 'erase'.
- Revise the 'read' command to always load EEPROM data from device
  to memory.

Signed-off-by: Curt Brune <curt@cumulusnetworks.com>
Accton u-boot sys_eeprom: Adjust patch chunks after revising common codes

Signed-off-by: Curt Brune <curt@cumulusnetworks.com>