New u-boot-aspeed-sdk runs slow and cause wdt2 timeout on ast2500

[Lei Yu]

On the latest master with u-boot-aspeed v00.04.09 SDK, an issue occurs
on g220a that it runs slower than before and gets wdt2 timeout.
We reverted the u-boot to a version before v00.04.09 SDK (b0fe8fd9d)
and the issue is gone.

Below are some details:
* Before v00.04.09: u-boot works OK, and it takes about 9~10 seconds
to load and start the kernel including the 2 seconds timeout for
autoboot, the kernel starts OK and it kicks the watchdog as long as
the driver is loaded.
* With v00.04.09: u-boot runs slower than before, and it takes about
**16 seconds** to load and start the kernel (including 2s timeout for
autoboot), then the kernel does not have enough time to run and loads
the watchdog driver, and the wdt2 times out on about 22s.

Be noted that the issue is observed on g220a that is based on AST2500,
and could not be reproduced in QEMU. I think it could be reproduced on
other systems with AST2500.

-- 
BRs,
Lei YU