usb: kbd: don't use int xfers when polling via ctrl xfers

When CONFIG_SYS_USB_EVENT_POLL_VIA_CONTROL_EP is enabled, use a
GET_REPORT control transfer to retrieve the initial state of the
keyboard. This matches the technique used to poll the keyboard state.
This is useful since it eliminates the remaining use of interrupt
transfers from the USB keyboard driver, which allows it to work with
USB HCD that don't support interrupt transfers.

Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>