Hi @n_kkkkk
First, you can add SoC Support.
The lpc54xxx family exists, so you just need to modify
soc/nxp/lpc/lpc54xxx/soc.c
soc/nxp/lpc/soc.yml
soc/nxp/lpc/lpc54xxx/Kconfig.soc
soc/nxp/lpc/lpc54xxx/Kconfig
And add dts.
dts/arm/nxp/nxp_lpc546xx.dtsi
And Create a Custom Board Definition
Getting Started Guide — Zephyr Project Documentation
Hope this will help you.
BR
Harry