usb: kconfig: usb keyboard kconfig

Add Kconfig options for USB keyboard and use them for cm-fx6.

Cc: Marek Vasut <marex@denx.de>
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>
diff --git a/configs/cm_fx6_defconfig b/configs/cm_fx6_defconfig
index 07a84bb..f0fd48c 100644
--- a/configs/cm_fx6_defconfig
+++ b/configs/cm_fx6_defconfig
@@ -20,3 +20,5 @@
 CONFIG_USB_EHCI_HCD=y
 CONFIG_USB_EHCI_MX6=y
 CONFIG_USB_STORAGE=y
+CONFIG_USB_KEYBOARD=y
+CONFIG_SYS_USB_EVENT_POLL_VIA_CONTROL_EP=y