legacy: i386 is legacy, inform the user

When we dropped support for i386, we added the corresponding opiton to
the legacy menu, but forgot to select BR2_LEGACY.

Fix that.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Config.in.legacy

@@ -189,6 +189,7 @@ config BR2_TOOLCHAIN_EXTERNAL_CODESOURCERY_POWERPC_E500V2
 
 config BR2_x86_i386
 	bool "x86 i386 support removed"
+	select BR2_LEGACY
 	help
 	  The support for the i386 processors of the x86 architecture
 	  has been removed.