drm/msm/dp: Initialize the INTF_CONFIG register

Some bootloaders set the widebus enable bit in the INTF_CONFIG register,
but configuration of widebus isn't yet supported ensure that the
register has a known value, with widebus disabled.

Fixes: c943b494

 ("drm/msm/dp: add displayPort driver support")
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20210722024434.3313167-1-bjorn.andersson@linaro.org
Signed-off-by: Rob Clark <robdclark@chromium.org>