Documentation: Update APM X-Gene clock binding for v2 hardware

Update APM X-Gene clock binding documentation for SoC and
PCP PLL for v2 hardware.
Signed-off-by: Loc Ho <lho@apm.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

Documentation/devicetree/bindings/clock/xgene.txt

@@ -9,6 +9,8 @@ Required properties:
 	"apm,xgene-socpll-clock" - for a X-Gene SoC PLL clock
 	"apm,xgene-pcppll-clock" - for a X-Gene PCP PLL clock
 	"apm,xgene-device-clock" - for a X-Gene device clock
+	"apm,xgene-socpll-v2-clock" - for a X-Gene SoC PLL v2 clock
+	"apm,xgene-pcppll-v2-clock" - for a X-Gene PCP PLL v2 clock
 
 Required properties for SoC or PCP PLL clocks:
 - reg : shall be the physical PLL register address for the pll clock.