ARM: OMAP1: dmtimer: conversion to platform devices

Convert OMAP1 dmtimers into a platform devices and then registers with
device model framework so that it can be bound to corresponding driver.

Signed-off-by: Thara Gopinath <thara@ti.com>
Signed-off-by: Tarun Kanti DebBarma <tarun.kanti@ti.com>
Reviewed-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Cousson, Benoit <b-cousson@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>