ipmi: Add Loongson-2K BMC support

This patch adds Loongson-2K BMC IPMI support.

According to the existing design, we use software simulation to
implement the KCS interface registers: Stauts/Command/Data_Out/Data_In.

Also since both host side and BMC side read and write kcs status, fifo flag
is used to ensure data consistency.

The single KCS message block is as follows:

+-------------------------------------------------------------------------+
|FIFO flags| KCS register data | CMD data | KCS version | WR REQ | WR ACK |
+-------------------------------------------------------------------------+

Co-developed-by: Chong Qiao <qiaochong@loongson.cn>
Signed-off-by: Chong Qiao <qiaochong@loongson.cn>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Acked-by: Corey Minyard <corey@minyard.net>
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Message-ID: <8f9ffb6f0405345af8f04193ce1510aacd075e72.1756987761.git.zhoubinbin@loongson.cn>
Signed-off-by: Corey Minyard <corey@minyard.net>