conf,qemu: implement RISC-V 'aia' virt domain feature

conf,qemu: implement RISC-V 'aia' virt domain feature

This feature is implemented as a string that can range from "none",
"aplic" and "aplic-imsic".

If the feature isn't present in the domain XML the hypervisor default
will be used. For QEMU, at least up to 9.2, the default is "none".

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>