develop a framework to dynamically enable required services depends on the running hardware platform

[ishidawataru]

Goldstone uses the ONL build system to build the ONIE image.
ONL build system builds the rootfs per CPU architecture.
If the CPU architecture is the same, the same rootfs is used for all supported platform.

Currently, Goldstone only supports 3 platforms. Galileo1, Cassini, and Galileo FlexT.

Galileo1 and Cassini have an amd64 CPU board, whereas Galileo FlexT has an arm64 CPU board.

Since Galileo1 and Cassini require the same set of services to enable, current Goldstone doesn't have a framework to dynamically switch the services to enable.

However, in order to support more hardware platforms, we'll need a framework to dynamically enable required services depending on the running hardware platform.

(Moreover, we may want a mechanism to create different rootfs per hardware platform when the ONIE installer writes the rootfs to the mass storage of the device. This requires improvement in ONL)

Currently, /var/lib/goldstone/device/$PLATFORM/init.sh runs before systemd starts. Galileo1 and Galileo FlexT are using this file to enable systemd services that are required to run in this file.

• https://github.com/oopt-goldstone/goldstone-buildimage/blob/master/packages/platforms/wistron/arm64/wtp-01-c1-00/goldstone-platform-config/PKG.yml#L20
• https://github.com/oopt-goldstone/goldstone-buildimage/blob/master/packages/platforms/wistron/arm64/wtp-01-c1-00/goldstone-platform-config/builds/init.sh

We need a structured way of doing this to make supporting a new platform easier.