ANDROID: f2fs: fix fscrypt direct I/O support

The upstream change to make f2fs use iomap for direct I/O was backported
to this kernel branch, which broke the out-of-tree support for fscrypt
direct I/O because f2fs_iomap_begin() isn't aware of encryption.  Make
the needed change to f2fs_iomap_begin(), matching what I've proposed
upstream at
https://lore.kernel.org/r/20220120071215.123274-5-ebiggers@kernel.org

.

Also drop the fscrypt support from fs/direct-io.c, which is no longer
used since both ext4 and f2fs now use iomap for direct I/O.

Bug: 162255927
Bug: 215554521
Fixes: 9ce28978 ("Merge remote-tracking branch 'aosp/upstream-f2fs-stable-linux-5.15.y' into android13-5.15")
Change-Id: I6b99b623ad3b8a86099c260787b2086b415a0e12
Signed-off-by: Eric Biggers <ebiggers@google.com>