hw/loongarch/virt: Set iocsr address space per-board rather than percpu

hw/loongarch/virt: Set iocsr address space per-board rather than percpu

LoongArch system has iocsr address space, most iocsr registers are
per-board, however some iocsr register spaces banked for percpu such
as ipi mailbox and extioi interrupt status. For banked iocsr space,
each cpu has the same iocsr space, but separate data.

This patch changes iocsr address space per-board rather percpu,
for iocsr registers specified for cpu, MemTxAttrs.requester_id
can be parsed for the cpu. With this patches, the total address space
on board will be simple, only iocsr address space and system memory,
rather than the number of cpu and system memory.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20231215100333.3933632-3-maobibo@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>