defconfig: msm8974: Enable USB to announce new devices

Add CONFIG_USB_ANNOUNCE_NEW_DEVICES=y to allow the USB host
subsystem to announce new devices in the syslog when connected.
This should have been added when the other USB host config items
were enabled on the msm8974 target, but somehow it was forgotten.

Change-Id: I0fa9d10d10fdaa88c739450a3bb394e46e907b01
Signed-off-by: Jack Pham <jackp@codeaurora.org>