ARM: OMAP: timer: obey the !CONFIG_OMAP_32K_TIMER

Currently, omap2_sync32k_clocksource_init() function initializes the 32K
timer as the system clock source regardless of the CONFIG_OMAP_32K_TIMER
setting.
Fix this by providing a default implementation for
!CONFIG_OMAP_32K_TIMER case.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
Reviewed-by: Paul Walmsley <paul@pwsan.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: stable@vger.kernel.org
Signed-off-by: Tony Lindgren <tony@atomide.com>