spi: cadence_qspi: add device tree binding doc

This patch adds the device tree binding doc for the cadence qspi controller &
also removes the not needed properties from the stv0991 device tree.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
Reviewed-by: Jagannadh Teki <jteki@openedev.com>

arch/arm/dts/stv0991.dts

@@ -32,11 +32,7 @@
 			reg = <0x80203000 0x100>,
 				<0x40000000 0x1000000>;
 			clocks = <3750000>;
-			ext-decoder = <0>; /* external decoder */
-			num-cs = <4>;
-			fifo-depth = <256>;
 			sram-size = <256>;
-			bus-num = <0>;
 			status = "okay";
 
 			flash0: n25q32@0 {
@@ -48,7 +44,6 @@
 				m25p,fast-read;
 				page-size = <256>;
 				block-size = <16>; 	/* 2^16, 64KB */
-				read-delay = <4>;	/* delay value in read data capture register */
 				tshsl-ns = <50>;
 				tsd2d-ns = <50>;
 				tchsh-ns = <4>;

doc/device-tree-bindings/spi/spi-cadence.txt

@@ -0,0 +1,28 @@
+Cadence QSPI controller device tree bindings
+--------------------------------------------
+
+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).
+- sram-size		: spi controller sram size.
+- status		: enable in requried dts.
+
+connected flash properties
+--------------------------
+
+- spi-max-frequency	: Max supported spi frequency.
+- page-size		: Flash page size.
+- block-size		: Flash memory block size.
+- 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.
+- tsd2d-ns		: Delay in master reference clocks (ref_clk) between one
+			  chip select being de-activated and the activation of
+			  another.
+- tchsh-ns		: Delay in master reference clocks between last bit of
+			  current transaction and de-asserting the device chip
+			  select (n_ss_out).
+- tslch-ns		: Delay in master reference clocks between setting
+			  n_ss_out low and first bit transfer