riscv: hw: Remove not needed PLIC properties in device tree

riscv: hw: Remove not needed PLIC properties in device tree

This removes "reg-names" and "riscv,max-priority" properties of the
PLIC node from device tree.

Signed-off-by: Bin Meng <[email protected]>
Reviewed-by: Jonathan Behrens <[email protected]>
Reviewed-by: Alistair Francis <[email protected]>
Signed-off-by: Palmer Dabbelt <[email protected]>