iwlwifi: add support for suspend-resume flow for new device generation

The new device generation has a slightly different suspend resume flow
Currently, the way the driver instruct the device to move to D3 is by
sending D3_CONFIG_CMD.
Instead of using the host command the indication is by writing to the
doorbell interrupt.
The FW will respond with interrupt to indicate transition completion.

Signed-off-by: Haim Dreyfuss <haim.dreyfuss@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>