kernel-yocto: respect SRC_URI modified branch selection

kernel-yocto: respect SRC_URI modified branch selection

Although the setting of KBRANCH is the suggested/primary way to interact with
the yocto kern-tools and the fetcher, some users may be more comfortable
modifying the SRC_URI branch parameter directly.

If they do, the tools will not force their branch and build output will be
different then they expect, in non obvious ways.

It's easy enough to detect this scenario, but checking the SRC_URI in the
same way that the git fetcher checks for the branch (and SRCREV). If we take
the value from the SRC_URI and use it directly in the patch/validate/update
routines, we'll stay consistent with KBRANCH if it is used, and also
automatically adapt to a manually changed branch parameter on the SRC_URI.

For all other users, there are no visible or behavioural changes as a result
of this change

(From OE-Core rev: cfce8643ed166b51d7178be173677ea6f527d453)

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>