OMAP: PM: DMA context save/restore for off-mode support

For HS/EMU devices, these additional features are also used:

- DMA interrupt disable routine added
- Added DMA controller reset to DMA context restore

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