Noticed that this class file name is "image_types.bbclass" and not
"image-types.bbclass". Fixed it.
(From yocto-docs rev: 354aa820a13f2dcff32e8a24cbce477c3d6b54f6)
Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>