ext4 crypto: do not select from EXT4_FS_ENCRYPTION

This patch adds a tristate EXT4_ENCRYPTION to do the selections
for EXT4_FS_ENCRYPTION because selecting from a bool causes all
the selected options to be built-in, even if EXT4 itself is a
module.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/Kconfig

@@ -64,8 +64,8 @@ config EXT4_FS_SECURITY
 	  If you are not using a security module that requires using
 	  extended attributes for file security labels, say N.
 
-config EXT4_FS_ENCRYPTION
-	bool "Ext4 Encryption"
+config EXT4_ENCRYPTION
+	tristate "Ext4 Encryption"
 	depends on EXT4_FS
 	select CRYPTO_AES
 	select CRYPTO_CBC
@@ -81,6 +81,11 @@ config EXT4_FS_ENCRYPTION
 	  efficient since it avoids caching the encrypted and
 	  decrypted pages in the page cache.
 
+config EXT4_FS_ENCRYPTION
+	bool
+	default y
+	depends on EXT4_ENCRYPTION
+
 config EXT4_DEBUG
 	bool "EXT4 debugging support"
 	depends on EXT4_FS