tool: Keil: Parse .o file as object file

The *.o file does not have the correct type number in Keil.py, it will
be set as text file which can not link by Keil.

Change-Id: Ib32e315c35e08ac0c882d5b4927948469fd9d0c9
Signed-off-by: Karl Zhang <karl.zhang@arm.com>

tools/keil.py

@@ -51,6 +51,9 @@ def _get_filetype(fn):
     if fn.rfind('.lib') != -1:
         return 4
 
+    if fn.rfind('.o') != -1:
+        return 3
+
     # other filetype
     return 5