yocto-bsp: use rstrip() for assignment lines

strip() isn't necessary and causes unintended formatting changes in
the output; rstrip() remove the trailing newlines as intended while
leaving indenting whitespace intact.

(From meta-yocto rev: 0caa6cd8c094b531ee8e78154dbf5a8e6014d1fd)

Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/bsp/engine.py

@@ -658,7 +658,7 @@ class SubstrateBase(object):
         """
         Expand all tags in a line.
         """
-        expanded_line = AssignmentLine(line.strip())
+        expanded_line = AssignmentLine(line.rstrip())
 
         while start != -1:
             end = line.find(CLOSE_TAG, start)