ARM: OMAP: dmtimer: pm_runtime support

Add pm_runtime feature to dmtimer whereby *_runtime_get_sync()
is called within omap_dm_timer_enable(), pm_runtime_put()
is called in omap_dm_timer_disable(). In addition to calling
pm_runtime_enable, we are calling pm_runtime_irq_safe so that
they can be called from interrupt context.

Signed-off-by: Tarun Kanti DebBarma <tarun.kanti@ti.com>
Signed-off-by: Partha Basak <p-basak2@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>