Hi,
Sorry, this is not supported directly. We have done some basic experiments with the 2-core LPC43xx devices and the biggest problem we encountered was that the 2 cores required 2 separate copies of the C library (compiled for 2 slightly different instruction sets) that could not be easily merged into a single ELF file, so the current out-of-the-box support it limited to the M4 core.
As a workaround, please consider following the legacy device tutorial to create a project manually (or simply import one of the code examples from NXP) and then edit the OpenOCD configuration script for the MCU to leave out only the M0 target (or use Segger J-Link and pick “LPCxxxx_M0” as the target device). Although, due to the limitations of the gdb, you won’t be able to easily debug both cores at the same time.