[nrf fromtree] doc: releases: Add not about CONFIG_UART_n_GPIO_MANAGEMENT removal

Add note that those Kconfig options were removed from Nordic UART driver
configuration.

Signed-off-by: Krzysztof Chruściński <[email protected]>
(cherry picked from commit 3a4c5a9)

Author: nordic-krch

doc/releases/release-notes-4.0.rst

@@ -228,6 +228,8 @@ Drivers and Sensors
 * Serial
 
   * LiteX: Renamed the ``compatible`` from ``litex,uart0`` to :dtcompatible:`litex,uart`.
+  * Nordic: Removed ``CONFIG_UART_n_GPIO_MANAGEMENT`` Kconfig options (where n is an instance
+    index) which had no use after pinctrl driver was introduced.
 
 * SPI