media: qcom: camss: Restrict endpoint bus-type to D-PHY

Currently the Qualcomm CAMSS driver only supports D-PHY while the
hardware on most SoCs also supports C-PHY. Until this support is added,
check for D-PHY to make it somewhat explicit that C-PHY won't work.

Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Tested-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
Reviewed-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Bryan O'Donoghue <bod@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>