RV_PLIC module is to manage multiple interrupt events generated from the peripherals. It implements Platform-Level Interrupt Controller in RISC-V Privileges specification Section 7.
The tool is to create register hjson file given values of number of sources,
number of targets, and max value of priority. By default target is 1 and
priority is 7 (8 level of priorities supported)
To change the value and to re-create hjson,
$ reg_rv_plic.py -s 64 -t 2 -p 15 rv_plic_reg.tpl.hjson > rv_plic_reg.hjson