This code reads the PLL configuration registers and correctly programs
things so the UART and such can come up.
There's MIPS74k platform issues that need fixing; but this at least brings
things up enough to echo stuff out the serial port and allow for interactive
debugging with ddb.
Tested:
* AR71xx SoCs
* AR933x SoC
* AR9344 board (DB120)
Obtained from: Qualcomm Atheros; Linux/OpenWRT
