[documentation]Add USB host support in documentation

Signed-off-by: Aurelian Zanoschi <aurelian17@gmail.com>
(cherry picked from commit 48d081265d06d14090f3b22c44f712a603116fba)
Signed-off-by: Ricardo Salveti <ricardo@foundries.io>

docs/extra-build-config.md

@@ -269,6 +269,15 @@ local.conf:
 
     ENABLE_DWC2_PERIPHERAL = "1"
 
+## Enable USB host support
+
+By default in case of the Compute Module 4 IO Board the standard USB driver
+that usually supports host mode operations is disabled for power saving reasons.
+Users who want to use the 2 USB built-in ports or the other ports provided via
+the header extension should set the following in local.conf:
+
+    ENABLE_DWC2_HOST = "1"
+
 ## Enable Openlabs 802.15.4 radio module
 
 When using device tree kernels, set this variable to enable the 802.15.4 hat: