samples: net: mqtt: Enable Wi-Fi cred for 54L too

This sample when used over Wi-Fi relies on Wi-Fi cred to provision AP
configuration persistently.

Fixes NCSIDB-1467.

Signed-off-by: Chaitanya Tata <[email protected]>

Author: krish2718

samples/net/mqtt/boards/nrf54l15dk_nrf54l15_cpuapp.conf

@@ -11,6 +11,9 @@ CONFIG_LOG_MODE_IMMEDIATE=y
 # Wi-Fi
 CONFIG_WIFI=y
 CONFIG_WIFI_NRF70=y
+CONFIG_WIFI_CREDENTIALS=y
+# Needed for Wi-Fi credentials
+CONFIG_SETTINGS=y
 
 # WPA supplicant
 CONFIG_WIFI_NM_WPA_SUPPLICANT=y