x86/platform/uv: Add new uv_sysfs platform driver

Add the uv_sysfs driver to construct a read-only sysfs interface at
/sys/firmware/sgi_uv/ to expose information gathered from UV BIOS. This
information includes:

  * UV Hub descriptions, including physical location
  * Cabling layout between hubs on the fabric
  * PCI topology, including physical location of PCI cards

Together, the information provides a robust physical description of a UV
system, useful for correlating to performance data or performing remote
support.

Signed-off-by: Justin Ernst <justin.ernst@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/20201125175444.279074-4-justin.ernst@hpe.com