Two fixes for x86:
- Unbreak stack dumps for inactive tasks by interpreting the special
first frame left by __switch_to_asm() correctly. The recent change not
to skip the first frame so ORC and frame unwinder behave in the same
way caused all entries to be unreliable, i.e. prepended with '?'.
- Use cpumask_available() instead of an implicit NULL check of a
cpumask_var_t in mmio trace to prevent a Clang build warning