power: reset: ltc2952: make trigger delay configurable

Make trigger delay configurable through device tree with
trigger-delay-ms property.

Trigger delay is the time to wait before starting shutdown
sequence after trigger line assertion.
Trigger delay must take into account the OFFT time configured
with the capacitor connected to OFFT pin of the LTC2952 chip.
Basically, the higher the capacitance connected to OFFT pin,
the larger trigger delay must be.

Signed-off-by: Marek Czerski <ma.czerski@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

power: reset: ltc2952: document optional trigger behavior

Document the fact that the trigger signal is now optional, and describe
the behavior when this is used.

While at it, fix a typo, and paraphrase a sentence to be less platform
specific.

Signed-off-by: Frans Klaver <frans.klaver@xsens.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>

Documentation: DT: Add LTC2952 poweroff bindings

LTC2952 is an external power control chip, which signals
the OS to shut down. This patch documents the DT binding
for the chip.

Signed-off-by: René Moll <rene.moll@xsens.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>