This enables support for xHCI host controller on Exynos5
and further disables EHCI support, to make sure only one
host controller is enabled at a time, since right now
using two controllers at a time is not possible with
current usb core infrastructure.

Anyone who wants to enable EHCI support again needs to
enable CONFIG_USB_EHCI, CONFIG_USB_EHCI_EXYNOS once again
in exynos5-dt config.

Signed-off-by: Vikas C Sajjan <vikas.sajjan@samsung.com>
Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>
Cc: Julius Werner <jwerner@chromium.org>
Cc: Simon Glass <sjg@chromium.org>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Cc: Dan Murphy <dmurphy@ti.com>
Cc: Marek Vasut <marex@denx.de>