Add developer option to convert from FDE to FBE

This set of changes adds the screen that offers this conversion,
and the plumbing so the option is only available on suitable
devices.

It does not implement the conversion mechanism.

Change-Id: Idbe5ef5d5fad197cc8187e1b288c57feef2c2c0b
diff --git a/fs_mgr/include/fs_mgr.h b/fs_mgr/include/fs_mgr.h
index 27fccf7..eb0a7fc 100644
--- a/fs_mgr/include/fs_mgr.h
+++ b/fs_mgr/include/fs_mgr.h
@@ -102,6 +102,7 @@
 int fs_mgr_is_verified(const struct fstab_rec *fstab);
 int fs_mgr_is_encryptable(const struct fstab_rec *fstab);
 int fs_mgr_is_file_encrypted(const struct fstab_rec *fstab);
+int fs_mgr_is_convertible_to_fbe(const struct fstab_rec *fstab);
 int fs_mgr_is_noemulatedsd(const struct fstab_rec *fstab);
 int fs_mgr_is_notrim(struct fstab_rec *fstab);
 int fs_mgr_is_formattable(struct fstab_rec *fstab);