[RFC] make sandbox UT more generic

Hi,

I'm working on implementing SCMI-based pinctrl/gpio driver, and want to re-use sandbox UT to test the code. However, It is somehow sandbox-specific (with additional DT nodes). How can/should we make it more generic for other targets/drivers rather than just by copying the test code? (I have already created a test for pinmux since there is only one existing scenario, but gpio test has many.)

Even if I say 'generic', my case may be special since real hardware (device drivers) cannot always run all the test cases, while SCMI-based drivers potentially can with a dummy SCMI server for sandbox. See: drivers/firmware/scmi/sandbox-scmi_agent.c

Thanks, -Takahiro Akashi