Unify the 64MiB flash layout

[Lei Yu]

This email is to share some information about the OpenBMC 64MiB flash layout.

In current Linux kernel, there is openbmc-flash-layout-64.dtsi that is
being used on meta-bytedance/meta-g220a system, there is on-going
change[1] for aspeed-bmc-ampere-mtjade.dts to use the layout as well.

However, according to ast2600's change[2], the layout does not fit
ast2600's u-boot, so it updates the layout by changing the existing
one.

On g220a system, we have tested the new layout and verifies that it
works fine, with below changes
1. Pick the ast2600's change[2] in kernel;
2. Pick the `image_types_phosphor.bbclass` change[3];
3. Update the u-boot env to boot from the new location, or use the new
u-boot-aspeed-sdk_2019.04.bb[4]
   On g220a, we use the new u-boot.

With the above changes, g220a system works fine with the new u-boot
and the updated flash layout.

To make it consistent for both ast2500 and ast2600, it's better to use
the same flash layout (and u-boot).
So I would suggest merge the changes of [1] and [3], for now g220a and
meta-ampere/meta-jade could be impacted.

[1]: https://lore.kernel.org/openbmc/20210517040036.13667-4-quan@os.amperecomputing.com/
[2]: https://lore.kernel.org/linux-arm-kernel/20210316085932.2601-1-troy_lee@aspeedtech.com/
[3]: https://gerrit.openbmc-project.xyz/c/openbmc/meta-phosphor/+/39343
[4]: https://github.com/openbmc/openbmc/blob/master/meta-aspeed/recipes-bsp/u-boot/u-boot-aspeed-sdk_2019.04.bb

-- 
BRs,
Lei YU