ar8216: factor out info whether switch should be configured at probe stage to ar8xxx_chip

Factor out info whether switch should be configured at probe stage
to ar8xxx_chip. Remove related chip_is_... checks.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43466 3c298f89-4303-0410-b956-a3cf2f4a3e73