ARM: OMAP: dmtimer: platform driver

Add dmtimer platform driver functions which include:
(1) platform driver initialization
(2) driver probe function
(3) driver remove function

Signed-off-by: Tarun Kanti DebBarma <tarun.kanti@ti.com>
Signed-off-by: Thara Gopinath <thara@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>