net: move Broadcom SF2 driver to Kconfig

net: move Broadcom SF2 driver to Kconfig

move to Kconfig:
	CONFIG_BCM_SF2_ETH
	CONFIG_BCM_SF2_ETH_DEFAULT_PORT
	CONFIG_BCM_SF2_ETH_GMAC

Also modified defconfigs of all platforms that use these configs.

Signed-off-by: Suji Velupillai <[email protected]>
Tested-by: Suji Velupillai <[email protected]>
Reviewed-by: JD Zheng <[email protected]>
Reviewed-by: Scott Branden <[email protected]>
Signed-off-by: Steve Rae <[email protected]>
Reviewed-by: Tom Rini <[email protected]>
Acked-by: Joe Hershberger <[email protected]>