sunxi: Select CONFIG_CMD_NET and CONFIG_CMD_SETEXPR by default

Select CONFIG_CMD_NET and CONFIG_CMD_SETEXPR by default rather then
needing to have this in every sunxi defconfig file.

This also fixes the Merrii_A80_Optimus defconfig no longer building.

Cc: Maxin B. John <maxin.john@enea.com>
Reported-by: Maxin B. John <maxin.john@enea.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>