clk: iproc: Extend binding to cover BCM63138

Broadcom BCM63138 DSL SoCs have the same ARMPLL clocking infrastructure
as the Cygnus and iProc chips, add a dedicated compatible string and
document that the ARMPLL node is a valid node for this chip.

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

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

···
     ch3_unused	lcpll_ports	4	BCM_NS2_LCPLL_PORTS_CH3_UNUSED
     ch4_unused	lcpll_ports	5	BCM_NS2_LCPLL_PORTS_CH4_UNUSED
     ch5_unused	lcpll_ports	6	BCM_NS2_LCPLL_PORTS_CH5_UNUSED
+
+BCM63138
+--------
+PLL and leaf clock compatible strings for BCM63138 are:
+    "brcm,bcm63138-armpll"