spi: dt-binding: document Microchip CoreSPI

spi: dt-binding: document Microchip CoreSPI

Add device tree bindings for Microchip's CoreSPI controller.

CoreSPI is a "soft" IP core intended for FPGA implementations. Its
configurations are set in Libero. These properties represent
non-discoverable configurations determined by Verilog parameters to the
IP.

Signed-off-by: Prajna Rajendra Kumar <prajna.rajendrakumar@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20251114104545.284765-3-prajna.rajendrakumar@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>