vt82c686: Set user_creatable=false for VT82C686B_PM

This device is part of the multifunction VIA superio/south bridge chip
so not useful in itself.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-Id: <d0a806fed5e8055aee4fcf5b2f4790e6dd0f9dc6.1610223397.git.balaton@eik.bme.hu>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>