drm/i915: Dual link needs Shutdown and Turn on packet for both ports

drm/i915: Dual link needs Shutdown and Turn on packet for both ports

For dual link MIPI panels, SHUTDOWN packet needs to send to both Ports
A & C during MIPI encoder disabling sequence. Similarly, TURN ON packet
to be sent to both Ports during MIPI encoder enabling sequence.

v2: Address review comments by Jani
    - Used a for loop instead of do-while loop.

v3: Used for_each_dsi_port macro instead of for loop

Signed-off-by: Gaurav K Singh <gaurav.k.singh@intel.com>
Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>