fscrypt: Handle support for v1 encryption policy

FS_IOC_ADD_ENCRYPTION_KEY ioctl need to support both
v1 policy with 'key_descriptor' as well along with
v2 encryption policy.

Change-Id: I7638191bc8926ba306b11c3e8a5dafdb3d396764
Signed-off-by: Phanindra Babu Pabba <pabba@codeaurora.org>