ARM: OMAP: dmtimer: switch-over to platform device driver

Register timer devices by going through hwmod database using
hwmod API. The driver probes each of the registered devices.
Functionality which are already performed by hwmod framework
are removed from timer code. New set of timers present on
OMAP4 are now supported.

Signed-off-by: Tarun Kanti DebBarma <tarun.kanti@ti.com>
Acked-by: Cousson, Benoit <b-cousson@ti.com>
[tony@atomide.com: folded in spinlock changes, left out is_omap2]
Signed-off-by: Tony Lindgren <tony@atomide.com>