drm/i915: MIPI Timings related changes for dual link

hactive, hfp, hbp, hsync needs to be halved for dual link MIPI Panels.
Accordingly timing related mmio regs needs to be programmed for both MIPI Ports.

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>