Support rpmsg-lite

1. Adjust the driver configuration of RISC-V PLIC in BL808 DTS. 🐛
2. Support C906/E907 communication through rpmsg-lite component. 🎉
3. Memory optimization, the remaining RAM is 43MB when the complete system is running. 💥

If you want to test the rpmsg-lite function, please enter the "kldload rpmsg_lite" command in the C906 terminal.