Add a debug knob debug.acpi.avoid.paths, a variant of debug.acpi.avoid

Add a debug knob debug.acpi.avoid.paths, a variant of debug.acpi.avoid
but without totally disabling execution of _INI and _STA.  Maybe useful
to narrow down the portion of namespace causing problems without messing
with editing and compiling ASL.  Disablement of _INI and _STA when
debug.acpi.avoid is specified has been added years before to workaround
interpreter crash on some systems, and I'm not sure whether the recent
ACPI-CA code still crashes on those systems, but I'll leave it as is
anyway for compatibility with FreeBSD.

Suggested-by: Sepherosa Ziehau