rockchip: firefly: Add some macros to enable the usb keyboard

Add four macros of CONFIG_USB_KEYBOARD,CONFIG_DM_KEYBOARD,etc in the
firefly-rk3288_defconfig,can support usb keyboard device when these four
macros are enabled.
Signed-off-by: NLeo Wen <leo.wen@rock-chips.com>
Acked-by: NPhilipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: NPhilipp Tomsich <philipp.tomsich@theobroma-systems.com>

configs/firefly-rk3288_defconfig

@@ -76,3 +76,7 @@ CONFIG_CONSOLE_SCROLL_LINES=10
 CONFIG_USE_TINY_PRINTF=y
 CONFIG_CMD_DHRYSTONE=y
 CONFIG_ERRNO_STR=y
+CONFIG_USB_KEYBOARD=y
+CONFIG_DM_KEYBOARD=y
+CONFIG_SYS_USB_EVENT_POLL=y
+CONFIG_SYS_STDIO_DEREGISTER=y