Many IPMB devices don't support smbus protocol and this driver
only supports the smbus protocol at the moment.

Added support for the i2c protocol as well. There will be a variable
"i2c-protocol" passed by the device tree or ACPI table which determines
whether the protocol is i2c or smbus.
Signed-off-by: Vijay Khemka <vijaykhemka@fb.com>
Reviewed-by: Asmaa Mnebhi <asmaa@mellanox.com>
Message-Id: <20191211185604.1266063-1-vijaykhemka@fb.com>
[IPMB.txt had moved to driver-api/ipmb.rst, I adjusted]
Signed-off-by: Corey Minyard <cminyard@mvista.com>