populate_sdk_base: Update extraction script for multilibs

populate_sdk_base: Update extraction script for multilibs

When multilibs are enabled, there will be more then one environment
file created.  We need to be sure to process each environment file.
The next function can simply use the last environment file processed
to get the magic value(s) that it requires.

(From OE-Core rev: 6f0537c835c35dcff5154de0bec066ec3e71a4f8)

Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>