ot1200: remove superfluous "string" tag

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Masahiro Yamada <yamada.m@jp.panasonic.com>

board/bachmann/ot1200/Kconfig

 if TARGET_OT1200
 
 config SYS_CPU
-	string
 	default "armv7"
 
 config SYS_BOARD
-	string
 	default "ot1200"
 
 config SYS_VENDOR
-	string
 	default "bachmann"
 
 config SYS_SOC
-	string
 	default "mx6"
 
 config SYS_CONFIG_NAME
-	string
 	default "ot1200"
 
 endif