target/riscv: Implement AIA CSRs for 64 local interrupts on RV32

The AIA specification adds new CSRs for RV32 so that RISC-V hart can
support 64 local interrupts on both RV32 and RV64.

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: 20220204174700.534953-11-anup@brainfault.org
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>