arm: omap2: timer: limit hwmod usage to non-DT boots

now that we have a working 32k clocksource driver,
we can limit HWMOD usage to non-DT boots and rely
on clocksource_of_init() every time we boot
with DT.

While at that, also make sure that we don't disable
the 32-counter device so it gets probed by its driver.

Signed-off-by: Felipe Balbi <balbi@ti.com>