CPUID dump check test case

This adds a new test function to the cpuid.py test module, where the
CPUID data exposed by QEMU is compared with a full CPUID dump extracted
previously.

The new test code ensures that there are no ABI changes for a given
machine-type + CPU model combination, between QEMU versions.

There are some known QEMU bugs and past ABI changes that require
ignoring some differences. Those cases handled as rules that set
ignore_cpuid_leaves on qemu_cpu.cfg.