Select VIRT_TO_BUS directly where needed

In commit 887cbce0adea ("arch Kconfig: centralise ARCH_NO_VIRT_TO_BUS")
I introduced the config sybmol HAVE_VIRT_TO_BUS and selected that where
needed.  I am not sure what I was thinking.  Instead, just directly
select VIRT_TO_BUS where it is needed.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/Kconfig b/mm/Kconfig
index ae55c1e..3bea74f 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -286,8 +286,12 @@
 	default "1"
 
 config VIRT_TO_BUS
-	def_bool y
-	depends on HAVE_VIRT_TO_BUS
+	bool
+	help
+	  An architecture should select this if it implements the
+	  deprecated interface virt_to_bus().  All new architectures
+	  should probably not select this.
+
 
 config MMU_NOTIFIER
 	bool