Adds the SPI_HOST device model for ibex. The device specification is as per
[1]. The model has been tested on opentitan with spi_host unit tests
written for TockOS.

[1] https://docs.opentitan.org/hw/ip/spi_host/doc/



Signed-off-by: Wilfred Mallawa <wilfred.mallawa@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220303045426.511588-1-alistair.francis@opensource.wdc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>