dts: cadence_spi: Sync DT bindings with Linux

dts: cadence_spi: Sync DT bindings with Linux

Adopt the Linux DT bindings and clean-up duplicate
and unused values.

Fix indentation of the QSPI node in the keystone k2g
device tree.

Tested on TI K2G platform:
Tested-by: Vignesh R <[email protected]>
Tested on a socfpga-cyclonev board:
Tested-by: Simon Goldschmidt <[email protected]>
Signed-off-by: Jason Rush <[email protected]>
Reviewed-by: Jagan Teki <[email protected]>
Acked-by: Simon Goldschmidt <[email protected]>
Acked-by: Marek Vasut <[email protected]>