of/spi: Support specifying chip select as active high via device tree

The patch allows to specify that an SPI device needs an active high chip
select.

Signed-off-by: Wolfgang Ocker <weo@reccoware.de>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/Documentation/powerpc/booting-without-of.txt b/Documentation/powerpc/booting-without-of.txt
index de4063c..02ea9a9 100644
--- a/Documentation/powerpc/booting-without-of.txt
+++ b/Documentation/powerpc/booting-without-of.txt
@@ -1917,6 +1917,8 @@
 			inverse clock polarity (CPOL) mode
     - spi-cpha        - (optional) Empty property indicating device requires
 			shifted clock phase (CPHA) mode
+    - spi-cs-high     - (optional) Empty property indicating device requires
+			chip select active high
 
     SPI example for an MPC5200 SPI bus:
 		spi@f00 {