fscrypt: remove filesystem specific build config option

In order to have a common code base for fscrypt "post read" processing
for all filesystems which support encryption, this commit removes
filesystem specific build config option (e.g. CONFIG_EXT4_FS_ENCRYPTION)
and replaces it with a build option (i.e. CONFIG_FS_ENCRYPTION) whose
value affects all the filesystems making use of fscrypt.

Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
index e38039f..e2cfd33 100644
--- a/fs/ext4/Kconfig
+++ b/fs/ext4/Kconfig
@@ -103,10 +103,9 @@
 	depends on EXT4_FS
 	select FS_ENCRYPTION
 	help
-	  Enable encryption of ext4 files and directories.  This
-	  feature is similar to ecryptfs, but it is more memory
-	  efficient since it avoids caching the encrypted and
-	  decrypted pages in the page cache.
+	  This kconfig symbol is deprecated; now it just selects
+	  FS_ENCRYPTION.  Use CONFIG_FS_ENCRYPTION=y in new config
+	  files
 
 config EXT4_FS_ENCRYPTION
 	bool