binutils: rename BRANCH var

binutils: rename BRANCH var

If BRANCH is defined in local.conf then that name is used to d/l sources
for binutils. You will get this error:

Fetcher failure for URL: 'git://sourceware.org/git/binutils-gdb.git;branch=hardknott;protocol=git'. Unable to fetch URL from any source.

Rename to SRCBRANCH like glibc has to avoid the more common variable name BRANCH.

Signed-off-by: Armin Kuster <akuster808@gmail.com>
--
V2]
Remove commented out BINUPV and function

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