vt82c686: Make vt82c686-pm an I/O tracing region

vt82c686: Make vt82c686-pm an I/O tracing region

Previously just an empty RAM region was mapped on realize, now we add
an empty io range logging access instead. I think the pm timer should
be hooked up here but not sure guests need it. PMON on fuloong2e sets
a base address but does not seem to enable region; the pegasos2
firmware pokes some regs but continues anyway so don't know if
anything would make use of these facilities. Therefore this is just a
clean up of previous state for now and not intending to fully
implement missing functionality which could be done later if some
guests need it.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <cff9b2442d3e2e1cfbdcbc2dfbb559031b4b1cc1.1610223397.git.balaton@eik.bme.hu>
[PMD: Split original patch, this is part 1/4
      (make 'vt82c686-pm' an I/O tracing region)]
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>