powerpc/kconfig: remove CONFIG_6xx

CONFIG_6xx is not used anymore. Remove it.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/embedded6xx/Kconfig

@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 config EMBEDDED6xx
 	bool "Embedded 6xx/7xx/7xxx-based boards"
-	depends on 6xx && BROKEN_ON_SMP
+	depends on PPC_BOOK3S_32 && BROKEN_ON_SMP
 
 config LINKSTATION
 	bool "Linkstation / Kurobox(HG) from Buffalo"