net: dsa: b53: Fix module autoload

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/b53/b53_mmap.ko  | grep alias
$

After this patch:

$ modinfo drivers/net/dsa/b53/b53_mmap.ko  | grep alias
alias:          of:N*T*Cbrcm,bcm63xx-switchC*
alias:          of:N*T*Cbrcm,bcm63xx-switch
alias:          of:N*T*Cbrcm,bcm6368-switchC*
alias:          of:N*T*Cbrcm,bcm6368-switch
alias:          of:N*T*Cbrcm,bcm6328-switchC*
alias:          of:N*T*Cbrcm,bcm6328-switch
alias:          of:N*T*Cbrcm,bcm3384-switchC*
alias:          of:N*T*Cbrcm,bcm3384-switch

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>