target/riscv: Implement AIA local interrupt priorities

target/riscv: Implement AIA local interrupt priorities

The AIA spec defines programmable 8-bit priority for each local interrupt
at M-level, S-level and VS-level so we extend local interrupt processing
to consider AIA interrupt priorities. The AIA CSRs which help software
configure local interrupt priorities will be added by subsequent patches.

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>
Message-id: 20220204174700.534953-10-anup@brainfault.org
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>