misc/sgi-xp: remove SGI SN2 support

Note this also marks xp broken on ia64 now, as the UV support, which
was disable in generic kernels before actually never compiled due to
undefined uv_gpa_to_soc_phys_ram and uv_gpa_in_mmr_space symbols since
at least commit c2c9f115 ("x86: uv: update XPC to handle updated
BIOS interface").

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lkml.kernel.org/r/20190813072514.23299-11-hch@lst.de


Signed-off-by: Tony Luck <tony.luck@intel.com>