ARM: OMAP5: PM: handle device instance for for coldreset

OMAP5 and OMAP4 have different device instance offsets.

So to handle them properly, use a runtime detected instance offset
Other bit offsets and register offsets remained constant.

Creating a new function is not really worthwhile here as the logic
will be replicated without much benefit.

Signed-off-by: Nishanth Menon <nm@ti.com>
santosh.shilimkar@ti.com: Refreshed patch against 3.8
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>