mmc: rk_sdmmc: add platform hook for special pm ops during deepsleep

mmc: rk_sdmmc: add platform hook for special pm ops during deepsleep

  We register a platform hook and restore all of our regs if platform does
need to cutoff controller's power-supply during deepsleep in period of time.
Make sure your have added "controller-power-down" property AND comment out
"keep-power-in-suspend" in related dts file.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Xiaoyao <xiaoyao@rock-chips.com>
Reviewed-by: Chenjh <chenjh@rock-chips.com>
Tested-by: Chenjh <chenjh@rock-chips.com>