linux-yocto: explicitly export KMETA to scripts

linux-yocto: explicitly export KMETA to scripts

The kern-tools scripts can support a meta branch and directory of a name that
isn't "meta", but they need the name passed through the environment variable
KMETA. ensuring that KMETA is exported in the shell environment sets the stage
to support flexible meta branch name.

(From OE-Core rev: 9b90c8ace04c88ac6105f0bf686f9abc70fe8074)

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>