spi: dt-bindings: Add rk3528-spi compatible

This adds a compatible string for the SPI controller on RK3528.

Signed-off-by: Chukun Pan <amadeus@jmu.edu.cn>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20250520100102.1226725-2-amadeus@jmu.edu.cn


Signed-off-by: Mark Brown <broonie@kernel.org>