hw/riscv: virt: Add optional AIA IMSIC support to virt machine

hw/riscv: virt: Add optional AIA IMSIC support to virt machine

We extend virt machine to emulate both AIA IMSIC and AIA APLIC
devices only when "aia=aplic-imsic" parameter is passed along
with machine name in the QEMU command-line. The AIA IMSIC is
only a per-HART MSI controller so we use AIA APLIC in MSI-mode
to forward all wired interrupts as MSIs to the AIA IMSIC.

We also provide "aia-guests=<xyz>" parameter which can be used
to specify number of VS-level AIA IMSIC Guests MMIO pages for
each HART.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Signed-off-by: Anup Patel <anup@brainfault.org>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220220085526.808674-4-anup@brainfault.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>