fscrypt: updates on 4.15-rc4

Cherry-picked from origin/upstream-f2fs-stable-linux-4.14.y:

9d468a2b Revert "locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()"
13b237d1 fscrypt: move to generic async completion
a2985b1c crypto: introduce crypto wait for async op
4bb665c7 locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()
249c9041 fscrypt: new helper function - fscrypt_prepare_setattr()
91d09c05 fscrypt: new helper function - fscrypt_prepare_lookup()
9a24d618 fscrypt: new helper function - fscrypt_prepare_rename()
4bd6179f fscrypt: new helper function - fscrypt_prepare_link()
b811faac fscrypt: new helper function - fscrypt_file_open()
e9f57e37 fscrypt: new helper function - fscrypt_require_key()
b31ee2e1 fscrypt: remove unneeded empty fscrypt_operations structs
82cbed4c fscrypt: remove ->is_encrypted()
2edb5df1 fscrypt: switch from ->is_encrypted() to IS_ENCRYPTED()
cde1fbb0 fs, fscrypt: add an S_ENCRYPTED inode flag
8ec05db2 fscrypt: clean up include file mess

Change-Id: I8980613b8d5ffedf72ef2c91e1ae2eebb521ae19
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>