image.bbclass: Handle image base type dependency properly
When a base image type has an implicit dependency (from IMAGE_TYPEDEP)
this has to be taken into account. This is a regression introduced by
OE-Core:
c2dab18 (image: Create separate tasks for rootfs construction).
The issue has been found when building meta-fsl-arm based images which
does not include the rootfs image type explicitly in IMAGE_FSTYPES but
instead is added, using IMAGE_TYPEDEP, for the 'sdcard.gz' image.
Reported-by: Fabio Berton <fabio.berton@ossystems.com.br>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
