drm/msm/dp: promote irq_hpd handle to handle link training correctly

Some dongles require link training done at irq_hpd request instead
of plugin request. This patch promote irq_hpd handler to handle link
training and setup hpd_state correctly.

Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>