ARM: tegra: enable STDIO deregistration

At the very least when USB keyboard support is enabled, we need to enable
CONFIG_SYS_STDIO_DEREGISTER, so the "usb reset" is able to re-scan USB
ports and find new devices. Enable it everywhere per request from Simon
Glass.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>