spi: Add Socionext F_OSPI SPI flash controller driver

Introduce Socionext F_OSPI controller driver. This controller is used to
communicate with slave devices such as SPI Flash memories. It supports
4 slave devices and up to 8-bit wide bus, but supports master mode only.

This driver uses spi-mem framework for SPI flash memory access, and
can only operate indirect access mode and single data rate mode.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Link: https://lore.kernel.org/r/20221124003351.7792-3-hayashi.kunihiko@socionext.com
Signed-off-by: Mark Brown <broonie@kernel.org>