ARM: OMAP1: Fix warnings about enabling 32 KiHz timer

Fix "Enable 32kHz OS timer in order to allow sleep states in idle"
warning. We are now compiling in bothe MPU timer and 32 KiHz timer,
so this warning is only valid when MPU_TIMER is set and OMAP_DM_TIMER
is not set.

Signed-off-by: Tony Lindgren <tony@atomide.com>