ath79: ag71xx: Remove ar7240_set_addr and ag71xx_ar7240_start

ath79: ag71xx: Remove ar7240_set_addr and ag71xx_ar7240_start

The builtin switch has it's initial valid mac address(00:00:01:00:00:00).
Since the builtin switch is an independent device, setting mac address of gmac1 to builtin switch isn't a good idea and this makes it impossilbe to split builtin switch apart as an independent platform device.
Remove these functions and apply default VLAN during initialization as a preparation for further driver splitting.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>