powerpc/powernv: remove the nvlink support

This code was only used by the vfio-nvlink2 code, which itself had no
proper use.  Drop this huge chunk of code build into every powernv
or generic build.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210326061311.1497642-3-hch@lst.de