ANDROID: fscrypt: fix DUN contiguity with inline encryption + IV_INO_LBLK_32 policies

IV_INO_LBLK_32 policies introduced the possibility that logically
contiguous data blocks might not have contiguous DUNs (because of
potential DUN wraparound). As such, whenever a page is merged into a
bio, fscrypt_mergeable_bio() must be called to check DUN contiguity.

Further, fscrypt inline encryption does not handle the case when the DUN
wraps around within a page (which can happen when the data unit size !=
PAGE_SIZE). For now, we handle that by disallowing inline encryption
with IV_INO_LBLK_32 policies when the data unit size != PAGE_SIZE (and
dropping the now redundant check for this in fscrypt_dio_supported()).

Bug: 144046242
Change-Id: I9cb414fcc284b197b9d3d1b9643029c6b875df5a
Signed-off-by: Satya Tangirala <satyat@google.com>