arm64: dts: qcom: msm8916-pm8916: Mark always-on regulators

Some of the regulators must be always-on to ensure correct operation of
the system, e.g. PM8916 L2 for the LPDDR RAM, L5 for most digital I/O
and L7 for the CPU PLL (strictly speaking the CPU PLL might only need
an active-only vote but this is not supported for regulators in
mainline currently).

The RPM firmware seems to enforce that internally, these supplies stay
on even if we vote for them to power off (and there is no other
processor running). This means it's pointless to keep sending
enable/disable requests because they will just be ignored.
Also, drivers are much more likely to get a wrong impression of the
regulator status, because regulator_is_enabled() will return false when
there are no users, even though the regulator is always on.

Describe this properly by marking the regulators as always-on.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230510-msm8916-regulators-v1-8-54d4960a05fc@gerhold.net