drivers: remove the SGI SN2 IOC3 base support

The IOC3 is a multi-function chip seen on SGI SN2 and some SGI
MIPS systems.  This removes the last bit of SN2 specific support,
while the bits used by the mips ports are still around (and being
substantially rewritten at the moment).

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lkml.kernel.org/r/20190813072514.23299-14-hch@lst.de


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