dm: spi: Add soft_spi implementation

Add a new implementation of soft_spi that uses device tree to specify the
GPIOs. This will replace soft_spi_legacy for boards which use driver model.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
3 files changed