parisc/power: Fix power soft-off button emulation on qemu

parisc/power: Fix power soft-off button emulation on qemu

commit 6472036581f947109b20664121db1d143e916f0b upstream.

Make sure to start the kthread to check the power button on qemu as
well if the power button address was provided.
This fixes the qemu built-in system_powerdown runtime command.

Fixes: d0c219472980 ("parisc/power: Add power soft-off when running on qemu")
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v6.0+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>