rockchip: add NV12 bo creation support

rockchip: add NV12 bo creation support

This patch does alignment if needed on the width and height, but does
not expose this change to the public facing gbm_bo. It is expected that
framebuffer creation in the kernel with do alignment such that
applications don't have to have platform specific knowledge of alignment
requirements.

TEST=nv12_test
BUG=chromium:607241

Change-Id: I6138afb56537f516fac038ff4db39593c623fccd
Reviewed-on: https://chromium-review.googlesource.com/341010
Commit-Ready: Zach Reizner <zachr@chromium.org>
Tested-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Zach Reizner <zachr@chromium.org>