hw/intc/loongarch_extioi: Add extioi virt extension definition

hw/intc/loongarch_extioi: Add extioi virt extension definition

On LoongArch, IRQs can be routed to four vcpus with hardware extended
IRQ model. This patch adds the virt extension definition so that
the IRQ can route to 256 vcpus.

    1.Extended IRQ model:
                                    |
    +-----------+     +-------------|--------+     +-----------+
    | IPI/Timer | --> | CPUINTC(0-3)|(4-255) | <-- | IPI/Timer |
    +-----------+     +-------------|--------+     +-----------+
                            ^       |
                            |
                       +---------+
                       | EIOINTC |
                       +---------+
                        ^       ^
                        |       |
                 +---------+ +---------+
                 | PCH-PIC | | PCH-MSI |
                 +---------+ +---------+
                   ^      ^          ^
                   |      |          |
            +--------+ +---------+ +---------+
            | UARTs  | | Devices | | Devices |
            +--------+ +---------+ +---------+

    2.Virt extended IRQ model:

      +-----+    +---------------+     +-------+
      | IPI |--> | CPUINTC(0-255)| <-- | Timer |
      +-----+    +---------------+     +-------+
                        ^
                        |
                  +-----------+
                  | V-EIOINTC |
                  +-----------+
                   ^         ^
                   |         |
            +---------+ +---------+
            | PCH-PIC | | PCH-MSI |
            +---------+ +---------+
              ^      ^          ^
              |      |          |
       +--------+ +---------+ +---------+
       | UARTs  | | Devices | | Devices |
       +--------+ +---------+ +---------+

Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Message-Id: <20240528083855.1912757-2-gaosong@loongson.cn>