dts: cadence_spi: Update documentation for DT bindings
Update documentation to reflect adopting the Linux DT bindings.
Tested on TI K2G platform: Tested-by: Vignesh R <vigneshr@ti.com>
Tested on a socfpga-cyclonev board: Tested-by: Simon Goldschmidt <sgoldschmidt@de.pepperl-fuchs.com> Signed-off-by: Jason Rush <jarush@gmail.com> Reviewed-by: Jagan Teki <jagan@openedev.com> Acked-by: Simon Goldschmidt <sgoldschmidt@de.pepperl-fuchs.com> Acked-by: Marek Vasut <marex@denx.de>