Disable SMBus access while accessing Enviromnental Controller registers

Disable SMBus access while accessing Enviromnental Controller registers

Some chips support Environmental Controller access through SMBus.
On those chips, it is possible that an Embedded Controller accesses
Environmental Controller chip registers at any time. There is no real
means for synchronization. On banked chips, this can and will result in
access errors with unpredictable result.

Disable SMBus access while reading or writing environmental controller
registers to work around the problem.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>