OMAP3: PM: restore SRAM functions after off-mode.

Generalize the copy of SRAM functions into omap_push_sram_idle()
so it can be used on init but also after off-mode transitions.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>