[POWERPC] 8xx: Add pin and clock setting functions.

These let board code set up pins and clocks without having to
put magic numbers directly into the registers.

The clock function is mostly duplicated from the cpm2 version;
hopefully this stuff can be merged at some point.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>