ARM: OMAP4: PM: Move DPLL control apis to dpll.c

This patch moves all the dpll control api's to a
common file dpll.c. This is in preperation of omap4
support wherein most of these api's can be reused.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Benoit Cousson <b-cousson@ti.com>