hw/intc: ibex_plic: Convert the PLIC to use RISC-V CPU GPIO lines

hw/intc: ibex_plic: Convert the PLIC to use RISC-V CPU GPIO lines

Instead of using riscv_cpu_update_mip() let's instead use the new RISC-V
CPU GPIO lines to set the external MIP bits.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 0a76946981852f5bd15f0c37ab35b253371027a8.1630301632.git.alistair.francis@wdc.com