configs: e850-96: Enable USB host support

configs: e850-96: Enable USB host support

Exynos850 SoC has a dual-role USB controller which can be configured in
USB host role. As it's the only one USB controller on the board, it's
shared between "device" USB connector (micro-USB) and host USB
connectors. The hardware automatically powers on the host related parts
when the micro-USB cable (for device role) is being disconnected. Also,
as U-Boot lacks dynamic USB role switching capability, the only way to
switch the role at the moment is to modify "dr_mode" property in
U-Boot's device tree file here:

    dts/upstream/src/arm64/exynos/exynos850-e850-96.dts

This won't affect the dynamic role switching later in Linux kernel, as a
separate (different) device tree blob is provided to the kernel.

Enable the USB host support and corresponding commands to make it
functional in E850-96 board.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>