bap-tracing: add M68K trace support

[b1llow]

Summary

Add systematic M68K system-emulation support to the BAP tracing plugin.

• Map every QEMU M68K CPU model to a BAP machine profile and require the machine plugin argument for M68K.
• Keep the M68K architectural state observable at instruction boundaries, including condition flags, the PC, and FPIAR.
• Capture memory-access values with the width and byte order expected by BAP frames.
• Add tests for machine selection and memory-value conversion.

Atomic compare-exchange tracing

M68K is big-endian and normally runs on a little-endian host, so it uses the reverse-host-endian atomic helpers. Upstream QEMU currently passes the raw host-order cmpxchg return value to plugin callbacks and always reports newv as the write value, including when the comparison fails.

This PR converts the returned value to guest byte order and reports the actual post-operation value: newv after a successful comparison, or the unchanged old value after a failed comparison. This correction is not yet present in upstream QEMU master and is required for accurate M68K memory traces.

Validation

• Full GitHub Actions build
• tcg/libtcg_user.a and libbap_tracing.so builds
• bap-tracing-machine
• bap-tracing-mem-value

[Rot127]

Thanks for fixing the many bugs I added there.

@moste00 Please take a look as well.