hw/intc/loongarch_ipi: Add loongarch IPI support

hw/intc/loongarch_ipi: Add loongarch IPI support

Loongarch IPI is added here, it inherits from class
TYPE_LOONGSON_IPI_COMMON, and two interfaces get_iocsr_as() and
cpu_by_arch_id() are added for Loongarch 3A5000 machine. It can
be used when ipi is emulated in userspace with KVM mode.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
[PMD: Rebased and simplified]
Co-Developed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Tested-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Tested-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-Id: <20240805180622.21001-13-philmd@linaro.org>