ANDROID: fscrypt: fall back to filesystem-layer crypto when needed

When the filesystem is mounted with '-o inlinecrypt', make fscrypt fall
back to filesystem-layer crypto when inline crypto won't work, e.g. due
to the hardware not supporting the encryption algorithm.

When blk-crypto-fallback is disabled, this fixes '-o inlinecrypt' to not
break any fscrypt policies that would otherwise work.

This is needed for VtsKernelEncryptionTest to pass on some devices.

Bug: 137270441
Bug: 151100202
Test: 'atest vts_kernel_encryption_test' on Pixel 4 with the
      inline crypto patches backported, and also on Cuttlefish.
Change-Id: I3e730df4608efb12d7126d1a85faddcccb566764
Signed-off-by: Eric Biggers <ebiggers@google.com>