spi: add support for microchip "soft" spi controller

spi: add support for microchip "soft" spi controller

Introduce driver support for the Microchip FPGA CoreSPI IP.

This driver supports only Motorola SPI mode and frame size of 8-bits.
TI/NSC modes and wider frame sizes are not currently supported.

Signed-off-by: Prajna Rajendra Kumar <prajna.rajendrakumar@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20251114104545.284765-4-prajna.rajendrakumar@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>