target: default to i586 for x86

The i586 was introduced almost 20 years ago, and some software
(NPTL, libstdc++, ..) doesn't work nicely with i386 anymore, so
it is time to move on.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

target/Config.in.arch

@@ -232,7 +232,7 @@ endchoice
 choice
 	prompt "Target Architecture Variant"
 	depends on BR2_i386
-	default BR2_x86_i386
+	default BR2_x86_i586
 	help
 	  Specific CPU variant to use