Add OSAL submodule

OSAL is now in a separate repo.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>

Author: krish2718

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "sdk-nrfxlib"]
 	path = sdk-nrfxlib
 	url = https://github.com/nrfconnect/sdk-nrfxlib.git
+[submodule "nrf_wifi"]
+	path = nrf_wifi
+	url = https://github.com/zephyrproject-rtos/nrf_wifi.git

README.md

@@ -87,7 +87,8 @@ The source directory structure shall look like this:
 
     nrf70_bm_lib/         # nRF70 BM driver library
     sdk_nrfxlib/          # nRF Connect SDK nrfxlib
-      nrf_wifi/           # nRF70 Wi-Fi OS agnostic driver
+      nrf_wifi/           # nRF70 Wi-Fi firmware patch blobs
+    nrf_wifi/             # nRF Wi-Fi driver OS agnostic code
     samples/              # Sample applications
       radio_test_bm/      # Radio test sample application
       scan_bm/            # Scan sample application