arm64: defconfig: enable usb for hikey960

Signed-off-by: Fan Ning <fanning4@hisilicon.com>

Squashed with:

FIX: arm64: defconfig: update for USB

Signed-off-by: Fan Ning <fanning4@hisilicon.com>
Signed-off-by: Guodong Xu <guodong.xu@linaro.org>
[Squashing]
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>