net: dsa: bcm_sf2: Fix module autoload for OF registration
If the driver is built as a module, autoload won't work because the module
alias information is not filled. So user-space can't match the registered
device with the corresponding module.
Export the module alias information using the MODULE_DEVICE_TABLE() macro.
Before this patch:
$ modinfo drivers/net/dsa/bcm_sf2.ko | grep alias
alias: platform:brcm-sf2