beaglebone: move BBB-specific bits into a BBB config

Change-Id: If8551e362a15af83964a84a450f76293dc2b0cf0
diff --git a/board/czechlight/beaglebone/kconfig b/board/czechlight/beaglebone/kconfig
index 2871883..5dcd313 100644
--- a/board/czechlight/beaglebone/kconfig
+++ b/board/czechlight/beaglebone/kconfig
@@ -1 +1,5 @@
 CONFIG_OMAP_WATCHDOG=y
+
+# CONFIG_USB_ZERO is not set
+CONFIG_USB_CDC_COMPOSITE=m
+# CONFIG_USB_G_NOKIA is not set