arm: mx6: cm-fx6: switch to usb kbd polling via int queue

CONFIG_SYS_USB_EVENT_POLL_VIA_INT_QUEUE works better than
CONFIG_SYS_USB_EVENT_POLL_VIA_CONTROL_EP (keyboards that previously didn't
work such as Microsoft Comfort Curve 1000 now do work, and it's also faster).

Switch to CONFIG_SYS_USB_EVENT_POLL_VIA_INT_QUEUE.

Cc: Stefano Babic <sbabic@denx.de>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>