doc: releases: Document HL78xx modem updates for 4.4

Update migration guide for HL78xx Kconfig option renames and startup
time changes. Add release notes for new AT Shell and AirVantage FOTA
support.

Signed-off-by: Zafer SEN <zafersn93@gmail.com>

Author: zafersn

doc/releases/migration-guide-4.4.rst

@@ -163,6 +163,25 @@ Networking
   code cannot use POSIX APIs, then the relevant network API prefix needs to be added to the
   code calling a network API.
 
+Modem
+*****
+
+Modem HL78XX
+============
+
+* The Kconfig options related to HL78XX startup timing have been renamed in
+  :kconfig:option:`CONFIG_MODEM_HL78XX_DEV_*` as follows:
+
+  - ``MODEM_HL78XX_DEV_POWER_PULSE_DURATION`` → ``MODEM_HL78XX_DEV_POWER_PULSE_DURATION_MS``
+  - ``MODEM_HL78XX_DEV_RESET_PULSE_DURATION`` → ``MODEM_HL78XX_DEV_RESET_PULSE_DURATION_MS``
+  - ``MODEM_HL78XX_DEV_STARTUP_TIME`` → ``MODEM_HL78XX_DEV_STARTUP_TIME_MS``
+  - ``MODEM_HL78XX_DEV_SHUTDOWN_TIME`` → ``MODEM_HL78XX_DEV_SHUTDOWN_TIME_MS``
+
+* The default startup timing was changed from 1000 ms to 120 ms to improve
+  initialization reliability across all supported boards.
+
+  Applications depending on the previous defaults must update their configuration.
+
 Other subsystems
 ****************
 

doc/releases/release-notes-4.4.rst

@@ -118,6 +118,11 @@ New APIs and options
   * :dtcompatible:`jedec,mspi-nor` now allows MSPI configuration of read, write and
     control commands separately via devicetree.
 
+* Modem
+
+  * :kconfig:option:`CONFIG_MODEM_HL78XX_AT_SHELL`
+  * :kconfig:option:`CONFIG_MODEM_HL78XX_AIRVANTAGE`
+
 * NVMEM
 
   * Flash device support