scsi: csiostor: Add module softdep on cxgb4

Both cxgb4 and csiostor drivers run on their own independent Physical
Function. But when cxgb4 and csiostor are both being loaded in parallel via
modprobe, there is a race when firmware upgrade is attempted by both the
drivers.

When the cxgb4 driver initiates the firmware upgrade, it halts the firmware
and the chip until upgrade is complete. When the csiostor driver is coming
up in parallel, the firmware mailbox communication fails with timeouts and
the csiostor driver probe fails.

Add a module soft dependency on cxgb4 driver to ensure loading csiostor
triggers cxgb4 to load first when available to avoid the firmware upgrade
race.

Link: https://lore.kernel.org/r/1632759248-15382-1-git-send-email-rahul.lakkireddy@chelsio.com
Fixes: a3667aae

 ("[SCSI] csiostor: Chelsio FCoE offload driver")
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>