ANDROID: ext4, f2fs: enable direct I/O with inline encryption

ext4 and f2fs have traditionally not supported direct I/O on encrypted
files, since it's difficult to implement with the traditional
filesystem-layer encryption.  But when inline encryption is used
instead, it's straightforward to support direct I/O, as long as the I/O
is fully filesystem-block-aligned.  Add support for it by:

- Making the two generic direct I/O implementations in the kernel,
  __blockdev_direct_IO() and iomap_dio_rw(), set the encryption context
  on bios for inline-encrypted files.  __blockdev_direct_IO() is used by
  f2fs, and was used by ext4 in kernel v5.4 and earlier.  iomap_dio_rw()
  is used by ext4 in kernel v5.5 and later.

- Making ext4 and f2fs allow direct I/O to encrypted files (rather the
  current behavior of falling back to buffered I/O) when the file is
  using inline encryption and the I/O is fully filesystem-block-aligned.

Bug: 137270441
Change-Id: I4c8f7497eb8f829d03611d24281113d68c21d4d1
Signed-off-by: Eric Biggers <ebiggers@google.com>