doc: releases: Add note about de-deprecation in Nordic UART driver

Add note in release notes for v4.2 about de-deprecation of
CONFIG_CONFIG_UART_x_NRF_HW_ASYNC option.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>

Author: nordic-krch

doc/releases/release-notes-4.2.rst

@@ -1031,3 +1031,9 @@ Other notable changes
 
 * Updated TF-M to version 2.1.2 (from 2.1.1). The release notes can be found at:
   https://trustedfirmware-m.readthedocs.io/en/tf-mv2.1.2/releases/2.1.2.html
+
+* Reverted deprecation of receiver option in Nordic UART driver. Receiver mode which is using
+  additional TIMER peripheral to count received bytes was previously deprecated
+  (e.g. :kconfig:option:`CONFIG_CONFIG_UART_0_NRF_HW_ASYNC`). However, it turned out that this
+  previously mode is the only one that is capable of reliably receive data without Hardware
+  Flow Control so it should stay in the driver.