soc: ti: pm33xx: Move the am33xx_push_sram_idle to the top

Move the am33xx_push_sram_idle function to the top as a preparation
for rtc+ddr mode as the function will be called by multiple functions
currently present before it.

No functional changes.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>