omap: timer: Set dmtimer used as clocksource in autoreload mode

If CONFIG_OMAP_32K_TIMER is not selected and dmtimer is used as clocksource, the
timer stops counting once overflow occurs as it was not set in autoreload mode.
This results into timekeeping failure: for example, 'sleep 1' at the shell after
the timer counter overflow would hang.

This patch sets up autoreload when starting the clocksource timer which fixes
the above issue.

Signed-off-by: Hemant Pedanekar <hemantp@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>