libfscrypt: get the fscrypt kernel API declarations from linux/fs.h

bionic now has linux/fs.h from the 4.14 kernel, which has the fscrypt
kernel API declarations.  Replace the manual declarations in libfscrypt,
except for the mode numbers which are not supported by the upstream
kernel.

Test: built, booted device with f2fs encryption
Change-Id: I6c663813828e3e0639d9be4298bff2bd4ec36c66
1 file changed