doc: release/4.1: add bits about common architecture interface

This adds bits in the release note on changes in common
architecture interface, where the changes affect more than one
architectures.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

doc/releases/release-notes-4.1.rst

@@ -96,6 +96,8 @@ Removed APIs and options
 
 * The ``z_pm_save_idle_exit()`` PM API function has been removed.
 
+* Struct ``z_arch_esf_t`` has been removed. Use ``struct arch_esf`` instead.
+
 
 Deprecated APIs and options
 ===========================