CI: Change doc generation to use a more generic target

Rather than targeting a specific board, use a Qemu target, which should
make the docs fairly general. The generated devicetree will be minimal,
but users wishing to view these docs should be generating them for a
specific build anyway.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

.github/workflows/docs.yml

@@ -44,9 +44,9 @@ jobs:
         working-directory: zephyr-lang-rust
         run: |
           # Note that the above build doesn't set Zephyrbase, so we'll need to do that here.
-          west build -t rustdoc -b nrf52840dk/nrf52840 docgen
+          west build -t rustdoc -b qemu_cortex_m3 docgen
           mkdir rustdocs
-          mv build/rust/target/thumbv7em-none-eabi/doc rustdocs/nostd
+          mv build/rust/target/thumbv7m-none-eabi/doc rustdocs/nostd
           cp docs/top-index.html rustdocs/index.html
 
       - name: Build build documentation