hw/i2c: Implement NPCM7XX SMBus Module Single Mode

hw/i2c: Implement NPCM7XX SMBus Module Single Mode

This commit implements the single-byte mode of the SMBus.

Each Nuvoton SoC has 16 System Management Bus (SMBus). These buses
compliant with SMBus and I2C protocol.

This patch implements the single-byte mode of the SMBus. In this mode,
the user sends or receives a byte each time. The SMBus device transmits
it to the underlying i2c device and sends an interrupt back to the QEMU
guest.

Reviewed-by: Doug Evans<dje@google.com>
Reviewed-by: Tyrong Ting<kfting@nuvoton.com>
Signed-off-by: Hao Wu <wuhaotsh@google.com>
Reviewed-by: Corey Minyard <cminyard@mvista.com>
Message-id: 20210210220426.3577804-2-wuhaotsh@google.com
Acked-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>