hw/riscv: virt: Don't use a macro for the PLIC configuration

Using a macro for the PLIC configuration doesn't make the code any
easier to read. Instead it makes it harder to figure out what is going
on, so let's remove it.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20211022060133.3045020-1-alistair.francis@opensource.wdc.com