recipes: Remove PR = r0 from all recipes

Remove all PR = "r0" from all .bb files in oe-core. This was done
with the command sed -e '/^PR.*=.*r0\"/d' recipes*/*/*.bb -i

We've switching to the PR server, PR bumps are no longer needed and
this saves people either accidentally bumping them or forgetting to
remove the lines (r0 is the default anyway).

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
image_types: Improve dependency handling between types (and use for sum.jffs2)

We're seeing a pattern of one image type needing to depend on another
type. A good example is jffs2 and sum.jffs2. This patch makes sum.jffs2
depend on jffs2 which will then allow a EXTRA_IMGAGECMD to be set for
sum.jffs2 individually without changing the jffs2 command. This allows the
-pad option to be configured differently.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>