doc: releases: Rename Arm to Arc

Fixes a typo in the release notes where two 'Arm' entries were
present, and the first should have been 'Arc'.

Signed-off-by: Kevin Townsend <kevin.townsend@analog.com>

doc/releases/release-notes-3.5.rst

@@ -58,15 +58,15 @@ Kernel
 Architectures
 *************
 
+* ARC
+
 * ARM
 
   * Architectural support for Arm Cortex-M has been separated from Arm
     Cortex-A and Cortex-R. This includes separate source modules to handle
     tasks like IRQ management, exception handling, thread handling and swap.
     For implementation details see :github:`60031`.
 
-* ARM
-
 * ARM64
 
 * RISC-V