drm/msm/dp/dp_ctrl: Move 'tu' from the stack to the heap

'struct tu_algo_data' is huge ~400 Bytes.

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/msm/dp/dp_ctrl.c: In function ‘_dp_ctrl_calc_tu.constprop’:
 drivers/gpu/drm/msm/dp/dp_ctrl.c:938:1: warning: the frame size of 1184 bytes is larger than 1024 bytes [-Wframe-larger-than=]

Cc: Rob Clark <robdclark@gmail.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Chandan Uddaraju <chandanu@codeaurora.org>
Cc: Kuogee Hsieh <khsieh@codeaurora.org>
Cc: linux-arm-msm@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: freedreno@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>