target/riscv: Add AIA cpu feature

We define a CPU feature for AIA CSR support in RISC-V CPUs which
can be set by machine/device emulation. The RISC-V CSR emulation
will also check this feature for emulating AIA CSRs.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Signed-off-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Message-id: 20220204174700.534953-7-anup@brainfault.org
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.h

@@ -78,7 +78,8 @@ enum {
     RISCV_FEATURE_MMU,
     RISCV_FEATURE_PMP,
     RISCV_FEATURE_EPMP,
-    RISCV_FEATURE_MISA
+    RISCV_FEATURE_MISA,
+    RISCV_FEATURE_AIA
 };
 
 #define PRIV_VERSION_1_10_0 0x00011000