ppc4xx: Sequoia: Add chip_config command

This patch removes the Sequoia "bootstrap" command and replaces it
with the now common command "chip_config".

Please note that the patches with the dynamic PCI sync clock
configuration have to be applied, before this one should go in.
This is because Sequoia has 2 different bootstrap EEPROMs, and
the old bootstrap command configured different values depending
on the detected PCI async clock (33 vs. 66MHz). With the PCI sync
clock patches, this is not necessary anymore. The PCI sync clock
will be configured correctly on-the-fly now.

Signed-off-by: Stefan Roese <sr@denx.de>