spi: rockchip-sfc: add rockchip serial flash controller

Add the rockchip serial flash controller (SFC) driver.

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Signed-off-by: Jon Lin <jon.lin@rock-chips.com>
Tested-by: Peter Geis <pgwipeout@gmail.com>
Tested-by: Chris Morgan <macromorgan@hotmail.com>
Link: https://lore.kernel.org/r/20210812134546.31340-3-jon.lin@rock-chips.com


Signed-off-by: Mark Brown <broonie@kernel.org>