clk: bcm: Add BCM63138 clock support

BCM63138 has a simple clocking domain which is primarily the ARMPLL
clocking complex, from which the ARM (CPU), APB and AXI clocks would be
derived from.

Since the ARMPLL controller is entirely compatible with the iProc ARM
PLL, we just initialize it without additional parameters.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>