arm64: dts: ls1028a: add interrupt to Root Complex Event Collector

The legacy interrupt INT_A is hardwired to the event collector. RCEC is
bascially supported starting with v5.11. Having a correct interrupt, will
make RCEC at least probe correctly.

There are still issues with how RCEC is implemented in the RCiEP on the
LS1028A. RCEC will report an error, but it cannot find the correct
subdevice.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>