powerpc/8xx: Fix two CONFIG_8xx left behind

Commit 968159c003 ("powerpc/8xx: Getting rid of remaining use of
CONFIG_8xx") removed all but 2 references to 8xx in Kconfigs.

This patch removes the two remaining ones.

Fixes: 968159c003 ("powerpc/8xx: Getting rid of remaining use of CONFIG_8xx")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/8xx/Kconfig

@@ -91,7 +91,7 @@ endmenu
 #
 
 menu "MPC8xx CPM Options"
-	depends on 8xx
+	depends on PPC_8xx
 
 # This doesn't really belong here, but it is convenient to ask
 # 8xx specific questions.