boards: rename up_squared_adsp intel_adsp_cavs15

The Audio DSP is not specific to up_squared, so make it more generic.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/scripts/west_commands/sign.py b/scripts/west_commands/sign.py
index 37d0bd0..55e820e 100644
--- a/scripts/west_commands/sign.py
+++ b/scripts/west_commands/sign.py
@@ -393,7 +393,7 @@
 
     @staticmethod
     def edt_get_rimage_target(board):
-        if 'up_squared_adsp' in board:
+        if 'intel_adsp_cavs15' in board:
             return 'apl'
         if 'intel_adsp_cavs18' in board:
             return 'cnl'