drm/i915: Fix the pipe state timing mismatch warnings

Adjust the get transcoder timings for mipi dsi as per the
set timing calculations.

v2: Use the existing intel_get_pipe_timings and do the dsi
    specific adjustments in the encoder get_config hook.(Ville, Jani)

v3: Exclude VBLANK and HBLANK registers for dsi transcoder.

v4: Fix the incomplete conditional logic.

Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1556809862-31203-1-git-send-email-vandita.kulkarni@intel.com