[ARM] 4320/1: ixp4xx: cpu type detection stuff cleanup

Move IXP4XX cpu detection stuff in a separate include file and remove unused definition.

Signed-off-by: Vladimir Barinov <vbarinov@ru.mvista.com>
Signed-off-by: Ruslan Sushko <rsushko@ru.mvista.com>
Signed-off-by: Deepak Saxena <dsaxena@mvista.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>