Measure effects of power management
How much power does u-bmc draw at idle? How much can this be reduced with enabling power management in the Linux .config?
Some notes:
The aspeed kernel does not support much (any) power management. I do not think you would see any change by enabling power management in the config.
Double checking that only the required clocks are enabled would be an easy start. There are some clocks that are marked as required in drivers/clk/clk-aspeed.c that may not be required for your platform.
The CPU can be run at lower frequencies. Scaling this down after boot would be an interesting test.
The SDRAM can be configured to run at a slower clock speed. Measuring the performance impact (boot time?) and the reduction in power draw could inform a decision here.