The IPA driver uses the remoteproc SSR notifier now, rather than the
temporary IPA notification system used initially.  As a result it no
longer needs a property identifying the modem subsystem DT node.

Use GIC_SPI rather than 0 in the example interrupt definition.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>