target/riscv: Allow users to force enable AIA CSRs in HART

We add "x-aia" command-line option for RISC-V HART using which
allows users to force enable CPU AIA CSRs without changing the
interrupt controller available in RISC-V machine.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Signed-off-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Message-id: 20220204174700.534953-18-anup@brainfault.org
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.h

@@ -376,6 +376,7 @@ struct RISCVCPUConfig {
     bool mmu;
     bool pmp;
     bool epmp;
+    bool aia;
     uint64_t resetvec;
 };