drm/msm/dp: check drm driver status in configure_cb

When dp is connected during boot, there is a chance that
configure_cb is called before drm probe is finished and
cause host_init failure. Here we poll the value of
poll_enabled and wait until drm driver is ready.

Change-Id: I65b869a55e02ef5d4d958e7bef2a62f6823f9297
Signed-off-by: Xiaowen Wu <wxiaowen@codeaurora.org>