i2c: i801: Add support for the Process Call command

The Process Call command is implemented by the hardware since the very
first Intel 82801 chipset, and trivial to support. Oscar Romero
Matamala from the Georgia Institute of Technology told me it is needed
for an experiment his team is working on at the moment, so let's just
add support for it.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>