Add driver for the SiFive SPI controller
on the HiFive Unleashed board.
Signed-off-by: Palmer Dabbelt <palmer@sifive.com> Signed-off-by: Emil Renner Berthing <kernel@esmil.dk> Signed-off-by: Yash Shah <yash.shah@sifive.com> Signed-off-by: Mark Brown <broonie@kernel.org>