ARM: dts: BCM63xx: Add ARMPLL device tree nodes

Add the ARM PLL controller which comes standard with the Cortex-A9 found
on the BCM63138 SoCs. This is the same controller as the one found in
the Broadcom iProc architecture, however, we have a separate compatible
string to indicate the integration difference, since the hardware is
different.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>