usb: kbd: select SYS_STDIO_DEREGISTER

If SYS_STDIO_DEREGISTER is not selected and USB_KEYBOARD is selected
U-Boot cannot be built due to missing function stdio_deregister_dev.

So USB_KEYBOARD should select SYS_STDIO_DEREGISTER.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>