DT documentation for SPI controller added.
Signed-off-by: NPalmer Dabbelt <palmer@sifive.com>
Signed-off-by: NEmil Renner Berthing <kernel@esmil.dk>
Signed-off-by: NYash Shah <yash.shah@sifive.com>
Signed-off-by: NMark Brown <broonie@kernel.org>