Set USB PID based on kernel name

- Check uname for imx or mtk, and set the PID appropriately.
- Bail out if we don't match either.
- If we start to have multiple boards with the same kernel version,
we'll have to come up with a more clever way to handle this.

Change-Id: I98df4503646c23cc9f34fa9dcf027183c11c93a7

usr/bin/usb-gadget-start.sh

diff --git a/usr/bin/usb-gadget-start.sh b/usr/bin/usb-gadget-start.sh
index e3f293b..9f0c557 100755
--- a/usr/bin/usb-gadget-start.sh
+++ b/usr/bin/usb-gadget-start.sh
@@ -1,8 +1,17 @@
 #!/bin/bash
 
+KERNEL_VERSION="$(uname -r)"
+if [[ "${KERNEL_VERSION}" =~ imx ]]; then
+  PRODUCT_ID="0x9303"
+elif [[ "${KERNEL_VERSION}" =~ mtk ]]; then
+  PRODUCT_ID="0x9304"
+else
+  echo "Unknown device, not setting up gadget."
+  exit 1
+fi
+
 PRODUCT_STRING="Mendel"
 MANUFACTURER_STRING="Google,LLC"
-PRODUCT_ID="0x9303"
 VENDOR_ID="0x18d1"
 USB_VER="0x0200"
 DEV_CLASS="2"