The logic can be improved and the historical NOISO/NOHDD variables
moved into the class and out of common code.
The variables are also then removed in favour of directly controlling
the behaviour from IMAGE_FSTYPES in line with all the other image types.
(From OE-Core rev: a052caed563a09a01f5a3ea1f0477f379c05bee0)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>