Clocklib: generic clocks framework

Hi,

Here is a new version based upon suggestions from Haavard and Russell.

Changes since last post:
* Split struct clk into clk and clk_ops
* Hide most non-generic things into clock type specific structs wrapping
  struct clk.
* Provide at least partial documentation for structures and fields.
* Better /sys/kernel/debug/clock formatting
* Incorporates sa1100 and PXA patches.

-- 
With best wishes
Dmitry