setup: minor changes to machine list

- Pass column results to `expand` to eliminate tabs.

This enables easy copy/paste into markdown files for updating.

- Filter out QEMU machines.

We enable the QEMU machines from Yocto to be used for building but
they're not actively supported.  Remove them to reduce the noise
in the tool output.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I53c3f039cb36c705aa614627aeb40b20471c499c