[U-Boot] powerpc/mpc85xx: Increase image size

[York Sun]

Scott, et al.

I'd like to start the discussion to increase u-boot image size for some
mpc85xx targets. As we all know the reset vector is at the very end and
linking process start from the top. This gives us no good choice but to
use fixed image size. While we have more and more features, the size
increases inevitably. It's time to adjust the arbitrary size. We are now
using 512KB. Shall we go with 768KB, or even 1MB?

For the first step, I think we don't have to increase size for all
targets. We can adjust those with CONFIG_SYS_TEXT_BASE=0xeff80000. Those
are the most recent used. There are other targets which don't use NOR
flash boot method. They should be considered as well.

It is per board configuration. But it may be better if we keep them
consistent.

Please comment.

Regards,

York