ext4: use fscrypt_prepare_new_inode() and fscrypt_set_context()

Convert ext4 to use the new functions fscrypt_prepare_new_inode() and
fscrypt_set_context().  This avoids calling
fscrypt_get_encryption_info() from within a transaction, which can
deadlock because fscrypt_get_encryption_info() isn't GFP_NOFS-safe.

For more details about this problem, see the earlier patch
"fscrypt: add fscrypt_prepare_new_inode() and fscrypt_set_context()".

Link: https://lore.kernel.org/r/20200917041136.178600-4-ebiggers@kernel.org


Signed-off-by: Eric Biggers <ebiggers@google.com>