dts: nrf5340: add missing GPIOTE1 in secure DTSI

GPIOTE1 on the nRF5340 SoC is always accessible as a non-secure
peripheral. However, it is only defined in the non-secure DTSI file.
This is therefore a missing node in the secure DTSI file, since
non-secure addresses are accessible by secure software.

Move the node definition to a common include file and pull it into the
app core DTSI as well. To keep things clean, adjust the node labels so
that:

- 'gpiote0' and 'gpiote1' are defined in the secure DTSI
- 'gpiote0' is not defined in the non-secure DTSI
- 'gpiote' is defined in both secure and non-secure DTSIs
- 'gpiote' refers to the same node as 'gpiote0' in the secure DTSI
- 'gpiote' refers to the same node as 'gpiote1' in the non-secure DTSI

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>