Enable user mode SPI device support

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**Is your feature request related to a problem? Please describe.**

In Zephyr RTOS you can build for a POSIX-compliant system (ref: https://docs.zephyrproject.org/latest/boards/native/native_sim/doc/index.html). I primarily use WSL2 for development w/ Zephyr RTOS and would like to contribute support for SPI in POSIX systems, however, I noticed that `CONFIG_SPI` is disabled in the WSL2 kernel build. To be clear, this build target is mainly used for simulation which is why it is called `native_sim`.

**Describe the solution you'd like**

I'd like `CONFIG_SPI`, `CONFIG_SPI_SPIDEV` enabled, including any other KConfig's that make sense for this support (e.g. drivers for specific USB to SPI adapters). I'm not too picky on how these are toggled, as long as it is possible to have a `/dev/spidev*` :)

**Describe alternatives you've considered**

I've considered building the WSL2 kernel myself and will likely do this in the interim, however I feel like this could work "out-of-the-box".

Start with the WSL2 kernel configuration for the native_sim POSIX use case and inspect the requested CONFIG_SPI and CONFIG_SPI_SPIDEV options. Determine which additional KConfig options or USB-to-SPI drivers are needed. Done means SPI support is enabled out of the box and a /dev/spidev* device can be used.

Written by the indexing model from the issue text.