dt-bindings: Document Broadcom Hurricane 2 clocks

Add a Device Tree binding document for the Broadcom Hurricane 2 SoC
which is an iProc based system.

Acked-by: Jon Mason <[e-mail]>
Signed-off-by: Florian Fainelli <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Florian Fainelli <[e-mail]>

Documentation/devicetree/bindings/clock/brcm,iproc-clocks.txt

···
     ch1_audio  audiopll         2       BCM_CYGNUS_AUDIOPLL_CH1
     ch2_audio  audiopll         3       BCM_CYGNUS_AUDIOPLL_CH2
 
+Hurricane 2
+------
+PLL and leaf clock compatible strings for Hurricane 2 are:
+ "brcm,hr2-armpll"
+
+The following table defines the set of PLL/clock for Hurricane 2:
+
+    Clock	Source		Index	ID
+    ---		-----		-----	---------
+    crystal	N/A		N/A	N/A
+
+    armpll	crystal		N/A	N/A
+
+
 Northstar and Northstar Plus
 ------
 PLL and leaf clock compatible strings for Northstar and Northstar Plus are: