dm-default-key, f2fs, ICE: support dm-default-key with f2fs/ICE

This patch fixes assigning bi_crypt_key for moving data which was previously
encrypted by f2fs.

Note that, dm-default-key should not assign bi_crypt_key, if bi_crypt_skip is
set.

The sceanrios is:

1. write data with user key by f2fs
  -  ENC(KU, IVU, DATA)
2. log out user key
3. read data #1 w/o user key from LBA #a
4. dm-default-key assigns default key
  - DEC(KD, LBA#a, ENC(KU, IVU, DATA))
5. write data #1 w/o user key into LBA #b
6. dm-default-key assigns default key
  - ENC(KD, LBA#b, DEC(KD, LBA#a, ENC(KU, IVU, DATA)))
7. Read DATA out with valid logged-in user key
  - DEC(KU, IVU, ENC(KD, LBA#b, DEC(KD, LBA#a, ENC(KU, IVU, DATA))))

So, this patch introduces bi_crypt_skip to avoid 4. ~ 6 with right flow:
1. write data with user key by f2fs
  -  ENC(KU, IVU, DATA)
2. log out user key
3. read data #1 w/o user key from LBA #a
4. dm-default-key skip to assign default key
  - ENC(KU, IVU, DATA)
5. write data #1 w/o user key into LBA #b
6. dm-default-key skips to assign default key
  - ENC(KU, IVU, DATA)
7. Try to read DATA with valid logged-in user key
  - DEC(KU, IVU, ENC(KU, IVU, DATA))

Change-Id: I4a047ff0d019cd062bdf99e8e0b7cea243721fb7
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
Signed-off-by: Shivaprasad Hongal <shongal@codeaurora.org>
Signed-off-by: Barani Muthukumaran <bmuthuku@codeaurora.org>