arm64: dts: qcom: msm8939-sony-tulip: Allow disabling pm8916_l6

The vendor kernel from Sony does not have regulator-always-on for
pm8916_l6, so we should be able to disable it when setting up the
display properly. Since sony-tulip does not have display set up
currently it should be fine to let the regulator disable until then.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230530-msm8939-regulators-v1-4-a3c3ac833567@gerhold.net