ARM: OMAP4: PM: Add support for OMAP4 dpll api's

Most of the dpll api's from dpll.c are reused for OMAP4.
This patch does extend a few api's for OMAP4 support.

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