spi: cadence_qspi: use "cdns,qspi-nor" as compatible

Linux uses "cdns,qspi-nor" as compatible string for the cadence
qspi driver, so change driver, docs and all device trees.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
diff --git a/doc/device-tree-bindings/spi/spi-cadence.txt b/doc/device-tree-bindings/spi/spi-cadence.txt
index 74c8208..69e02c1 100644
--- a/doc/device-tree-bindings/spi/spi-cadence.txt
+++ b/doc/device-tree-bindings/spi/spi-cadence.txt
@@ -2,7 +2,7 @@
 --------------------------------------------
 
 Required properties:
-- compatible		: should be "cadence,qspi".
+- compatible		: should be "cdns,qspi-nor"
 - 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).