tegra: usb gadget: fix ci udc operation if not hostpc capable

The Tegra 2 aka T20 is not host PC capable. Therefore gate the define
CONFIG_CI_UDC_HAS_HOSTPC in tegra-common-usb-gadget.h in case of
CONFIG_TEGRA20.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>