OMAP3: PM: Enable SDRAM auto-refresh during sleep

Fix for ES3.0 bug: SDRC not sending auto-refresh when OMAP wakes-up
from OFF mode (warning for HS devices.)

Signed-off-by: Tero Kristo <tero.kristo@nokia.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>