gpu: host1x: mipi: Set MIPI_CAL_BIAS_PAD_CFG1 register

During calibration, sets the "internal reference level for drive pull-
down" to the value specified in the Tegra TRM.

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>