ixgbe: Fix IOSF SB access issues

IOSF is the Intel On-chip System Fabric used in SOCs. IOSF SB is
the IOSF SideBand message interface. This patch serializes IOSF SB
access using both phy bits in the SWFW_SEMAPHORE register. It also
adds a helper function to wait for IOSF SB accesses to complete.
Use the new function to perform this wait before each access, as
specified in the datasheet, in addition to using it to wait for
IOSF SB read/write completion.

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>