clocksource: convert OMAP1 to 32-bit down counting clocksource

Convert the OMAP1 32-bit down counting clocksource to the generic
clocksource infrastructure.

Tested-by: Tony Lindgren <tony@atomide.com>
Cc: linux-omap@vger.kernel.org
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>