usb: kbd: allow probing even if usbkbd not in stdin

For now the driver does not probe if usbkbd was not present in stdin.
This presents two issues, we can not probe the driver before setting stdin
and we can not use this driver in other manner than stdin console.

This patch fixes this by adding an else statement. It simply probes the
driver without console management in the case "usbkbd" is not in stdin.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>