Add "chip_config" command for PPC4xx bootstrap configuration

This patch adds a generic command for programming I2C bootstrap
eeproms on PPC4xx. An implementation for Canyonlands board is
included.

The command name is intentionally chosen not to be PPC4xx specific.
This way other CPU's/SoC's can implement a similar command under
the same name, perhaps with a different syntax.

Usage on Canyonlands:

=> chip_config
Available configurations (I2C address 0x52):
600-nor          - NOR  CPU: 600 PLB: 200 OPB: 100 EBC: 100
600-nand         - NAND CPU: 600 PLB: 200 OPB: 100 EBC: 100
800-nor          - NOR  CPU: 800 PLB: 200 OPB: 100 EBC: 100
800-nand         - NAND CPU: 800 PLB: 200 OPB: 100 EBC: 100
1000-nor         - NOR  CPU:1000 PLB: 200 OPB: 100 EBC: 100
1000-nand        - NAND CPU:1000 PLB: 200 OPB: 100 EBC: 100
1066-nor         - NOR  CPU:1066 PLB: 266 OPB:  88 EBC:  88 ***
1066-nand        - NAND CPU:1066 PLB: 266 OPB:  88 EBC:  88
=> chip_config 600-nor
Using configuration:
600-nor          - NOR  CPU: 600 PLB: 200 OPB: 100 EBC: 100
done (dump via 'i2c md 52 0.1 10')
Reset the board for the changes to take effect

Other 4xx boards will be migrated to use this command soon
as well.

Signed-off-by: Stefan Roese <sr@denx.de>
Signed-off-by: Dirk Eibach <eibach@gdsys.de>
Acked-by: Matthias Fuchs <matthias.fuchs@esd.eu>