x86/platform/uv: Add sysfs hubless leaves

Add uv_sysfs hubless leaves for UV hubless systems.

Signed-off-by: Mike Travis <mike.travis@hpe.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Steve Wahl <steve.wahl@hpe.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lkml.kernel.org/r/20201128034227.120869-4-mike.travis@hpe.com