Cadence QSPI controller device tree bindings
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Required properties:
- compatible		: should be "cadence,qspi".
- reg			: 1.Physical base address and size of SPI registers map.
			  2. Physical base address & size of NOR Flash.
- clocks		: Clock phandles (see clock bindings for details).
- cdns,fifo-depth	: Size of the data FIFO in words.
- cdns,fifo-width	: Bus width of the data FIFO in bytes.
- cdns,trigger-address	: 32-bit indirect AHB trigger address.
- cdns,is-decoded-cs	: Flag to indicate whether decoder is used or not.
- status		: enable in requried dts.

connected flash properties
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- spi-max-frequency	: Max supported spi frequency.
- page-size		: Flash page size.
- block-size		: Flash memory block size.
- cdns,tshsl-ns		: Added delay in master reference clocks (ref_clk) for
			  the length that the master mode chip select outputs
			  are de-asserted between transactions.
- cdns,tsd2d-ns		: Delay in master reference clocks (ref_clk) between one
			  chip select being de-activated and the activation of
			  another.
- cdns,tchsh-ns		: Delay in master reference clocks between last bit of
			  current transaction and de-asserting the device chip
			  select (n_ss_out).
- cdns,tslch-ns		: Delay in master reference clocks between setting
			  n_ss_out low and first bit transfer
