[nrf fromtree] doc: release: migration_guide: 4.5: Add note on SRAM Kconfig change

Adds details about this switching to Kconfig

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
(cherry picked from commit e4af38d)

Author: nordicjm

doc/releases/migration-guide-4.5.rst

@@ -32,6 +32,12 @@ Kernel
 Boards
 ******
 
+* The Kconfig options :kconfig:option:`CONFIG_SRAM_SIZE` and
+  :kconfig:option:`CONFIG_SRAM_BASE_ADDRESS` have been deprecated, boards should instead use the
+  devicetree ``zephyr.sram`` chosen node to specify the RAM node which will be used (whose values
+  populated the Kconfig values). If either option is manually adjusted, it will cause
+  :kconfig:option:`CONFIG_SRAM_DEPRECATED_KCONFIG_SET` to be set which indicates this deprecation.
+
 Device Drivers and Devicetree
 *****************************