linux-wrs: rename to linux-yocto

linux-wrs: rename to linux-yocto

The existing preferred yocto kernel wasn't named appropriately
and needs to be updated.

In keeping the changes small and isolated, this commit simply
renames the recipe and some internal variables. Future commits
will refactor the code into more usable blocks.

Now that linuy-wrs has been renamed linux-yocto, we need
to rename and update an board configurations and append
files.

Now that linux-wrs has been renamed linux-yocto, we need to
update the SRCREVs to have the new name.

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>