tests: add a QEMU-based test which emulates a mock MM8108, brings it up and does a scan

[dpgeorge]

This PR adds a new tests/qemu_driver test which emulates a mock MM8108 chipset and tests the following calls to the driver:

• mm_halow_wifi_set_up() (indirectly tests mm_halow_init())
• mm_halow_wifi_scan_cached()
• the scan result from a mock AP probe result is printed out

That tests quite a bit of the driver infrastructure and plumbing. It needs an SPI backend and the mock MM8108 needs to respond to a subset of the commands that the real hardware responds to.

The test prints out some things which are checked against test_bringup.exp, and that's run under CI. This should help prevent basic regressions in the driver. If the CI passes at least we know that a chip can be brought up.

I used Claude Code for most of this. It did a good job of writing the MM8108 emulator, based on SPI traces I captured from a real chip, along with it inspecting the mm-iot-sdk sources.

[kwagyeman]

Builds and passes here, fails correctly on a bad exit code or changed .exp. Note, chip_reg() has no bound check on its 16-entry table, add an abort at the end so it fails loudly if a future morselib touches more registers. Otherwise LGTM.