Add support for Cortex-M85

Rely on CMSIS code for initializing Cortex-M85 devices.

Fallback to mcpu=cortex-m55 for gcc until support for cortex-m85 is
available.

Change-Id: I8b47563c3f0f44e35735a569f2abf8a308948e67
diff --git a/targets/corstone-310/platform.ld b/targets/corstone-310/platform.ld
index 9d41f8f..a854afb 100644
--- a/targets/corstone-310/platform.ld
+++ b/targets/corstone-310/platform.ld
@@ -145,8 +145,8 @@
   {
     KEEP(*(.vectors))
     *crt* (.text*)
-    *startup_ARMCM55.c.obj (.text*)
-    *system_ARMCM55.c.obj (.text*)
+    *startup_ARMCM85.c.obj (.text*)
+    *system_ARMCM85.c.obj (.text*)
     *target.cpp.obj (.text*)
 
     KEEP(*(.init))