ixgbe: Add I2C bus mux support

Take control of an I2C mux that selects which SFP is attached to
the I2C bus. The control of the mux is captured in the taking and
releasing of the related semaphore. Because only port 1 can control
the mux, port 1 always leaves the mux set to select port 0.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>