spi: dt-bindings: snps,dw-apb-ssi.yaml: update compatible property

updated compatible property to include "thead,th1520-spi" for the
TH1520 SoC SPI Controller.

Signed-off-by: Kanak Shilledar <kanakshilledar@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20240701121355.262259-3-kanakshilledar@gmail.com


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