[Skiboot] [PATCH 2/2] astbmc: Use oem hiomap ipmi command for bmc_sw_ami

[Lei YU]

> How do we detect what firmware the BMC is running? Because it's a bit
> misleading to use the _ami struct when we've only tested OpenBMC.

Checking from code, there is no "openbmc" thing for ast2400, and there is not
really a "detection" of the BMC, it is hardcoded by each `<machine>.c`.
Skiboot "detects" the machine, which comes from `dt_root`.