omap2 clock: Standardize DPLL rate recalculation with struct dpll_data

Introduce a new data structure, struct dpll_data, that contains DPLL
multiplier, divider, and autoidle information.  Update existing DPLL code
to use struct dpll_data.  The goal here is to set up something that will be
usable for OMAP3430 clock tree.  Note that this does not affect the SRAM DPLL
assembly code - the DPLL register addresses are still hard-coded there.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>