defconfig: 8974: Enable required config for Host mode class support

Different class devices can be connected in USB Host mode. To support
device class like video, audio and ACM, enable required configs.
- CONFIG_USB_VIDEO_CLASS to connect USB video devices
- CONFIG_SND_USB_AUDIO to connect USB audio devices
- CONFIG_USB_ACM to support CDC ACM devices
- CONFIG_USB_USBNET to support CDC ECM devices

Hence enable all above configs to support different class devices
in USB Host mode.

Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>
Change-Id: I60b43389430d9df077cc81916abd50d8e3e81786