doc: migration: 4.2: Add note on HWMv1

Adds a note that HWMv1 support has now been dropped

Signed-off-by: Jamie McCrae <[email protected]>

Author: nordicjm

doc/releases/migration-guide-4.2.rst

@@ -23,6 +23,9 @@ the :ref:`release notes<zephyr_4.2>`.
 Build System
 ************
 
+* HWMv1 support has been removed, any out-of-tree boards or SoCs in HWMv1 format must be migrated
+  to :ref:`HWMv2 <hw_model_v2>` to work with Zephyr v4.2 onwards.
+
 Kernel
 ******