rockchip: Change keyboard input from CrOS EC keyboard to a USB keyboard

These boards aren't ChromeOS devices so won't have a cros-ec-keyb
input as it's the keyboard available via the ChromeOS Embedded
Controller. Update them to use a USB keyboard which would actually
be available. Also enable the usb keyboard option for those devices
that don't have it enabled already.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Reviewed-by: Michael Trimarchi <michael@amarulasolutions.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>