OMAP2+: clock: comment that osc_ck/osc_sys_ck should use clockfw autoidle control

Place some comments in the OMAP oscillator clock control code to note that
its autoidle mode should eventually be controlled via the new OMAP clockfw
autoidle control interface.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Tested-by: Rajendra Nayak <rnayak@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>