ANDROID: GKI: fscrypt: add OEM data to struct fscrypt_operations

'struct fscrypt_operations' shouldn't really be part of the KMI, as
there's no reason for loadable modules to use it.  However, due to the
way MODVERSIONS calculates symbol CRCs by recursively dereferencing
structures, changes to 'struct fscrypt_operations' affect the CRCs of
KMI functions exported from certain core kernel files such as
fs/dcache.c.  That brings it in-scope for the KMI freeze.

There is an OEM who wants to add fields to this struct, so add an
ANDROID_OEM_DATA_ARRAY for them to use.

Bug: 173475629
Change-Id: Idfc76884fce8a5fcc0837cd9363695d5428b1624
Signed-off-by: Eric Biggers <ebiggers@google.com>