u-boot branches

[Joel Stanley]

As Aspeed develop their ast2600 u-boot features, we've had a need to
integrate changes from their tree into the openbmc tree. In the past
we lined this up with a major version bump (as with the kernel),
meaning we could create a new branch with our "out of tree" changes
applied on top. However, in this case their SDK is still based on the
2019.04 release, so there's not a clear way forward.

I've chosen to rebase the openbmc changes on top of their branch. The
old branch is still accessible at archive/v2019.04-aspeed-openbmc-1.
The bitbake recipe will continue to work as it uses the nobranch=1
flag, and specifies the version based on the SHA.

The new branch contains their aspeed-master-v2019.04 tree as of today,
with the OpenBMC changes applied on top.

I've boot tested it running from SPI NOR on AST2600 A1 hardawre, as
well as QEMU, and it reached userspace. I will bump the bitbake recipe
to integrate the changes into openbmc.

Eddie, can you see what changes are required on top of this branch to
support eMMC boot, and rebase your patch series? Please include an
emmc boot defconfig based on ast2600_openbmc_spl_defconfig.

Cheers,

Joel