ARM: OMAP: add support for oscillator setup

This contains startup and shutdown times for the oscillator. By default
use ULONG_MAX. Oscillator setup is used for calculating and setting up
latencies for sleep modes that disable oscillator.

Based on a patch from Nishanth Menon <nm@ti.com>.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>