Use dizzy branch for poky and meta-openembedded layers

The upstream sources for poky and meta-openembedded have each forked a
dizzy branch to support the Yocto 1.7 "Dizzy" release.  In preparing
a Dizzy release, develop against the dizzy version of these layers by
switch from tracking master/master-next to dizzy.

After release, the dev branch of this manifest will go back to
tracking master/master-next for these layers.

Note: the other included layers, meta-ti and meta-ros don't have
      dizzy specific commits so just track master.

Signed-off-by: Ash Charles <ashcharles@gmail.com>