arm: tegra: exchange v_back_porch and v_front porch values

arm: tegra: exchange v_back_porch and v_front porch values

Bug 1450363

There is not enough spool up time for populating buffers with
the exisintg back porch. By exchanging front and back porch
values, we add more time while keeping the same pixel clock

Change-Id: I91c677b7cd2e603ac91905b9d4932b11b25cb836
Signed-off-by: Anshuman Nath Kar <anshumank@nvidia.com>
Reviewed-on: http://git-master/r/385204
Reviewed-by: Mrutyunjay Sawant <msawant@nvidia.com>
Tested-by: Mrutyunjay Sawant <msawant@nvidia.com>