dt-binding: ptp: Add SoC compatibility strings for dte ptp clock

Add SoC specific compatibility strings to the Broadcom DTE
based PTP clock binding document.

Fixed the document heading and node name.

Fixes: 80d60761 ("dt-binding: ptp: add bindings document for dte based ptp clock")
Signed-off-by: NArun Parameswaran <arun.parameswaran@broadcom.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/ptp/brcm,ptp-dte.txt

-* Broadcom Digital Timing Engine(DTE) based PTP clock driver
+* Broadcom Digital Timing Engine(DTE) based PTP clock
 
 Required properties:
-- compatible: should be "brcm,ptp-dte"
+- compatible: should contain the core compatibility string
+              and the SoC compatibility string. The SoC
+              compatibility string is to handle SoC specific
+              hardware differences.
+              Core compatibility string:
+                 "brcm,ptp-dte"
+              SoC compatibility strings:
+                 "brcm,iproc-ptp-dte" - for iproc based SoC's
 - reg: address and length of the DTE block's NCO registers
 
 Example:
 
-ptp_dte: ptp_dte@180af650 {
-	compatible = "brcm,ptp-dte";
+ptp: ptp-dte@180af650 {
+	compatible = "brcm,iproc-ptp-dte", "brcm,ptp-dte";
 	reg = <0x180af650 0x10>;
 	status = "okay";
 };