dt-bindings: wkup-m3-ipc: Add ti,set-io-isolation property

Add documentation for the ti,set-io-isolation DT property on the wkup_m3_ipc
node which tells the wkup_m3_ipc driver to use the wkup_m3 to enable
IO Isolation during low power mode transitions on am43xx platforms.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
[dfustini: convert to YAML, make DTS example that passes check]
Signed-off-by: Drew Fustini <dfustini@baylibre.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220414192722.2978837-2-dfustini@baylibre.com